Projection exposure apparatus

ABSTRACT

A projection exposure apparatus including an irradiation optical system including a light source and irradiating a mask with irradiation light beams, a projection optical system for projecting an image of a pattern of the mask on a substrate, a plurality of first fly-eye type optical integrators each having an emission side focal plane disposed on a Fourier transformed surface with respect to the pattern of the mask in the irradiation optical system or on a plane adjacent to the same and having a center located at a plurality of positions which are eccentric from the optical axis of the irradiation optical system, a plurality of second fly-eye type optical integrators each having an emission side focal plane disposed on a Fourier transformed plane with respect to the incidental end of each of a plurality of the first fly-eye type optical integrators or on a plane adjacent to the same and being disposed to correspond to a plurality of the first fly-eye type optical integrators, and a light divider for dividing and causing the irradiation light beams from the light source to be incident on each of a plurality of the second fly-eye type optical integrators.

This is a continuation of application Ser. No. 08/371,895 filed Jan. 12,1995, which is a continuation of application Ser. No. 07/942,193 filedSep. 9, 1992, both now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projection exposure apparatus for useto form a pattern of a semiconductor integrated circuit, or a liquidcrystal device, or the like.

2. Related Background Art

When a circuit pattern of a semiconductor device or the like is formed,so-called photolithography technology is required. In this process, amethod, in which a reticle (a mask) pattern is formed on a substratesuch as semiconductor wafer, is usually employed. The surface of thesubstrate is applied with photosensitive photoresist so that a circuitpattern is transferred to the photoresist in accordance with an imageirradiated with light, that is, in accordance with the shape of thepattern corresponding to a transparent portion of the reticle pattern.In a projection exposure apparatus (for example, a stepper), the imageof a circuit pattern drawn on the reticle so as to be transferred isprojected on the surface of the substrate (wafer) via a projectionoptical system so as to be imaged.

In an irradiation optical system for irradiating the reticle with light,an optical integrator such as a fly-eye type optical integrator (afly-eye lens) and a fiber is used so as to uniform the distribution ofthe intensities of irradiation light with which the surface of thereticle is irradiated. In order to make the aforesaid intensitydistribution uniform optimally, a structure which employs the fly-eyelens is arranged in such a manner that the reticle-side focal surface(the emission side) and the surface of the reticle (the surface on whichthe pattern is formed) hold a substantially Fourier transformedrelationship. Also the focal surface adjacent to the reticle and thefocal surface adjacent to the light source (the incidental side) holdthe Fourier transformed relationship. Therefore, the surface of thereticle, on which the pattern is formed, and the focal surface of thefly-eye lens adjacent to-the light source (correctly, the focal surfaceof each lens of the fly-eye lens adjacent to the light source) hold animage formative relationship (conjugated relationship). As a result ofthis, irradiation light beams from respective optical elements (asecondary light source image) of the fly-eye lens are added (superposed)because they pass through a condenser lens or the like so that they areaveraged on the reticle. Hence, the illuminance uniformity on thereticle can be improved. Incidentally, there has been disclosed anarrangement capable of improving the illuminance uniformity in U.S. Pat.No. 4,497,015 in which two pairs of optical integrators are disposed inseries.

In a conventional projection exposure apparatus, the light quantitydistribution of irradiation beams to be incident on the opticalintegrator, such as the aforesaid fly-eye lens, has been made to besubstantially uniform in a substantially circle area (or in arectangular area), the center of which is the optical system of theirradiation optical system.

FIG. 14 illustrates a schematic structure of a conventional projectionexposure apparatus (stepper) of the above described type. Referring toFIG. 14, irradiation beams L140 pass through a fly-eye lens 41c, aspatial filter (an aperture diaphragm) 5a and a condenser lens 8 so thata pattern 10 of a reticle 9 is irradiated with the irradiation beamsL140. The spatial filter 5a is disposed on, or adjacent to a Fouriertransformed surface 17 (hereinafter abbreviated to a "pupil surface")with respect to the reticle side focal surface 414c of the fly-eye lens41c, that is, with respect to the reticle pattern 10. Furthermore, thespatial filter 5a has a substantially circular opening centered at apoint on optical axis AX of a projection optical system 11 so as tolimit a secondary light source (plane light source) image to a circularshape. The irradiation light beams, which have passed through thepattern 10 of the reticle 9, are imaged on a resist layer of a wafer 13via the projection optical system 11. In the aforesaid structure, thenumber of apertures of the irradiation optical system (41c, 5a and 8)and the number of reticle-side apertures formed in the projectionoptical system 11, that is σ value is determined by the aperturediaphragm (for example, by the diameter of an aperture formed in thespatial filter 5a), the value being 0.3 to 0.6 in general.

The irradiation light beams L140 are diffracted by the pattern 10patterned by the reticle 9 so that 0-order diffracted light beam Do,+1-order diffracted light beam Dp and -1-order diffracted light beam Dmare generated from the pattern 10. The diffracted light beams Do, Dp andDm, thus generated, are condensed by the projection optical system 11 sothat interference fringes are generated. The interference fringes, thusgenerated, correspond to the image of the pattern 10. At this time,angle θ (reticle side) made by the 0-order diffracted light beam Do and±1-order diffracted light beams Dp and Dm is determined by an equationexpressed by sin θ=λ/P (ξ: exposure wavelength and P: pattern pitch).

It should be noted that sin θ is enlarged in inverse proportion to thelength of the pattern pitch, and therefore if sin θ has become largerthan the number of apertures (NA_(R)) formed in the projection opticalsystem 11 adjacent to the reticle 9, the ±1-order diffracted light beamsDp and Dm are limited by the effective diameter of a pupil (a Fouriertransformed surface) 12 in the projection optical system 11. As aresult, the ±1-order diffracted light beams Dp and Dm cannot passthrough the projection optical system 11. At this time, only the 0-orderdiffracted light beam Do reaches the surface of the wafer 13 andtherefore no interference fringe is generated. That is, the image of thepattern 10 cannot be obtained in a case where sin θ>NA_(R). Hence, thepattern 10 cannot be transferred to the surface of the wafer 13.

It leads to a fact that pitch P, which holds the relationship sin θ=λ/P≅NA_(R), has been given by the following equation.

    P≅λ/NA.sub.R                              ( 1)

Therefore, the minimum pattern size becomes about 0.5·λ/NA_(R) becausethe minimum pattern size is the half of the pitch P. However, in theactual photolithography process, some considerable amount of focal depthis required due to an influence of warp of the wafer, an influence ofstepped portions of the wafer generated during the process, and thethickness of the photoresist. Hence, a practical minimum resolutionpattern size is expressed by k·λ/NA_(R), where k is a process factorwhich is about 0.6 to 0.8. Since the ratio of the reticle side number ofarticles NA_(W) and the wafer side number of articles NA_(R) is the sameas the imaging magnification of the projection optical system, theminimum resolution size on the reticle is k·λ/NA_(R) and the minimumpattern size on the wafer is k·λ/NA_(W) =k·λ/B·NA_(R) (where B is animaging magnification (contraction ratio)).

Therefore, a selection must be made whether an exposure light sourcehaving a shorter wavelength is used or a projection optical systemhaving a larger number of apertures is used in order to transfer a moreprecise pattern. It might, of course, be considered feasible to study tooptimize both the exposure wavelength and the number of apertures.

However, it is so far difficult for the projection exposure apparatus ofthe above described type to shorten the wavelength of the irradiationlight source (for example, 200 nm or shorter) because a proper opticalmaterial to make a transmissive optical member is not present and soforth. Furthermore, the number of apertures formed in the projectionoptical system has approached its theoretical limit at present andtherefore it is difficult to further enlarge the apertures. Even if theaperture can be further enlarged, the focal depth expressed by ±λ/2NA²rapidly decreases with an increase in the number of apertures, causing acritical problem to take place in that the focal depth required in apractical use further decreases.

In Japanese Patent Publication No. 62-50811 for example, there has beendisclosed a so-called phase shift reticle arranged in such a manner thatthe phase of each of transmissive light beams traveled from specificpoints in the transmissive portions of the circuit pattern of thereticle is shifted by π from the phase of transmissive light beamstraveled from the other transmissive portions. By using a phase shiftreticle of the type described above, a further precise pattern can betransferred.

However, the phase shift reticle has a multiplicity of unsolved problemsbecause of a fact that the cost cannot be reduced due to its complicatedmanufacturing process and inspection and modification methods have notbeen established even now.

Hence, an attempt has been made as projection exposure technology whichdoes not use the phase shift reticle and with which the transferenceresolving power can be improved by modifying the method of irradiatingthe reticle with light beams. One irradiation method of the aforesaidtype is a so-called annular zone irradiation method, for example,arranged in such a manner that the irradiation light beams which reachthe reticle 9 are given a predetermined inclination by making thespatial filter 5a shown in FIG. 14 an annular opening so that theirradiation light beams distributed around the optical axis of theirradiation optical system are cut on the Fourier transformed surface17.

In order to establish projection exposure having a further improvedresolving power and a larger focal depth, an inclination irradiationmethod or a deformed light source method has been previously disclosedin PCT/JP91/01103 (filed on Aug. 19, 1991). The aforesaid irradiationmethod is arranged in such a manner that a diaphragm (a spatial filter)having a plurality (two or four) openings, which are made to beeccentric with respect to the optical axis of the irradiation opticalsystem by a quantity corresponding to the precision (the pitch or thelike) of the reticle pattern, is disposed adjacent to the emission-sidefocal surface of the fly-eye lens so that the reticle pattern isirradiated with the irradiation light beams from a specific directionwhile inclining the light beams by a predetermined angle.

However, the above mentioned inclination irradiation method and thedeformed light source method have a problem in that it is difficult torealize a uniform illuminance distribution over the entire surface ofthe reticle because the number of effective lens elements (that is, thenumber of secondary light sources capable of passing through the spatialfilter) decreases and therefore an effect of making the illuminanceuniform on the reticle deteriorates. What is worse, the light quantityloss is excessive large in the system which has a member, such as thespatial filter, for partially cutting the irradiation light beams.Therefore, the illumination intensity (the illuminance) on the reticleor the wafer can, of course, deteriorate excessively, causing a problemto take place in that the time taken to complete the exposure processbecomes long with the deterioration in the irradiation efficiency.Furthermore, a fact that light beams emitted from the light sourceconcentrically pass through the Fourier transformed plane in theirradiation optical system will cause the temperature of a lightshielding member, such as the spatial filter, to rise excessively due toits light absorption and a measure (air cooling or the like) must betaken to prevent the performance deterioration due to change in theirradiation optical system caused from heat.

In a case where a diaphragm of the aforesaid type is disposed adjacentto the emission side focal surface of the fly-eye lens, some of thesecondary light source images formed by a plurality of the lens elementsare able to superpose on the boundary portion between the lighttransmissive portion of the diaphragm and the light shielding portion ofthe same. This means a fact that the secondary light source imageadjacent to the aforesaid boundary portion is shielded by the diaphragmor the same passes through the boundary portion on the contrary. Thatis, an unstable factor, such as the irradiation light quantity, isgenerated and another problem arises in that the light quantities of thelight beams emitted from the aforesaid diaphragm and that are incidenton the reticle become different from one another. Furthermore, in theinclination irradiation method, the positions of the four openings (inother words, the light quantity distribution in the Fourier transformedsurface) must be changed in accordance with the degree of precision ofthe reticle pattern (the line width, or the pitch or the like).Therefore, a plurality of diaphragms must be made to be exchangeable inthe irradiation-optical system, causing a problem to arise in that thesize of the apparatus is enlarged.

When a secondary light source formed on the reticle side focal surfaceof the fly-eye lens is considered in a case where the light sourcecomprises a laser such as an excimer laser having a spatial coherence,the irradiation light beams corresponding to the lens elements have someconsiderable amount of coherence from each other. As a result, randominterference fringes (speckle interference fringes) are formed on thesurface of the reticle or the surface of the wafer which is in conjugatewith the surface of the reticle, causing the illuminance uniformity todeteriorate. When its spatial frequency is considered here, a Fouriercomponent corresponding to the minimum interval between the lenselements is present in main. That is, the number of combinations oflight beams contributing to the interference is the largest. Therefore,fringes having a relatively low frequency (having a long pitch) incomparison to the limit resolution and formed to correspond to theconfiguration direction of the lens elements are observed on the surfaceof the reticle or the surface of the wafer. Although the formedinterference fringes have low contrast because the KrF excimer laser hasa relatively low spatial coherence, the interference fringe acts asparasite noise for the original pattern. The generation of theinterference fringes causes a problem when the illuminance uniformity,which will be further required in the future, is improved. In the casewhere the annular zone irradiation method is considered, the aforesaidnoise concentrically superposes in the vicinity of thelimit resolution,and therefore the influence of the noise is relatively critical incomparison to the ordinary irradiation method (see FIG. 14).

SUMMARY OF THE INVENTION

An object of the present invention is to provide a projection exposureapparatus capable of obtaining high resolution and a large focal depthand revealing excellent illuminance uniformity even if an ordinaryreticle is used.

In the present invention, the emission side focal surface is disposed ona Fourier transformed surface 17 with respect to a mask in the opticalpath of the irradiation optical system or on a plane adjacent to thesame as shown in FIG. 1. Furthermore, there are a plurality of firstfly-eye lenses 41a and 41b the centers of which are disposed at aplurality of positions which are eccentric from optical axis AX of theirradiation optical system, a plurality of second fly-eye lenses 40a and40b having the emission side focal plane located on the Fouriertransformed surface with respect to each incidental end of a pluralityof the first fly-eye lenses 41a and 41b or on a surface adjacent to thesame and disposed to correspond to the first fly-eye lenses 41a and 41band light dividers for dividing the irradiation light beams from thelight source to be incident on a plurality of the second fly-eye lenses40a and 40b. Furthermore, a guide optical element is disposed so as tocause the light beams emitted from one of a plurality of the secondfly-eye lenses to be incident on one of a plurality of the first fly-eyelenses. In a case where a laser represented by an excimerlaser is usedas the light 1 source, an optical path difference generating member 70is disposed between a plurality of the light beams emitted from thelight dividers 20 and 21 shown in FIG. 17, the optical path differencegenerating member 70 causing an optical path difference (the phasedifference) longer than the coherent distance (the coherent length) ofthe irradiation light beams to be given.

As shown in FIGS. 24 and 27, the present invention comprises, in anirradiation optical path, a plane light source forming optical system100 or 106 and 107 for forming a plurality of light sources, aconverging optical system 102 or 108 for converging the light beams fromthe plane light source forming optical system, a polyhedron light sourceforming optical system 103 having a plurality of lens elements 103a to103d for forming a plurality of plane light source images on the Fouriertransformed surface with respect to the reticle by the light beams fromthe converging optical system or on a plane adjacent to the same andhaving the centers of the optical axes disposed at a optical axis of theirradiation optical system, and a condenser for converging the lightbeams from the plurality of plane light source images formed by thepolyhedron light source forming optical system onto the reticle.

In the aforesaid basic structure, assuming that half of the distancebetween the optical axes of the lens elements in a direction of thepattern of said reticle is L, the focal distance on the emission side ofsaid condenser lens is f, the wavelength of said irradiation light beamsis λ and the cyclic pitch of said pattern of said mask is P, it ispreferable to arrange the structure to satisfy the following condition:

    L=λf/2P

In a case where the reticle has a two-dimensional pattern, thepolyhedron light source forming optical system is composed of four lenselements disposed in parallel and, assuming that the number of apertureson the reticle side of said projection optical system is NA_(R), half ofthe distance between the optical axes of said lens elements 103a to 103din a direction of the pattern of the reticle is L, and the emission sidefocal distance of the condenser lens 8 is f, it is preferable that thefollowing conditions are satisfied:

    0.35NA.sub.R≦L/f≦ 0.7NA.sub.R

As shown in FIG. 29, the present invention comprises light dividers 200and 201 for dividing the irradiation light beams in the optical path ofthe irradiation optical system, polyhedron light source forming opticalsystems 202a, 202b, 203a, 203b, 204a and 204b for forming a plurality ofplane light sources which correspond to each light beam divided by thelight dividers on the Fourier transformed surface with respect to thereticle 9 or on a plane adjacent to the same at a plurality of positionswhich are eccentric from the optical axis of the irradiation opticalsystem and a condenser lens 8 for converging the light beams from aplurality of the plane light sources onto the reticle, wherein thepolyhedron light source forming optical system includes at least rodtype optical integrators 203a and 203b.

In the aforesaid basic structure, the polyhedron light source formingoptical system may have a plurality of rod type optical integrators thecenters of which are disposed at a plurality of positions which areeccentric from the optical axis of the irradiation optical system.

Furthermore, the polyhedron light source forming optical system maycomprise a first converging lens for converging light beams divided bythe light dividing optical system, a rod type optical integrator havingthe incidental surface disposed at the focal point of the converginglens and a second converging lens for converging the light beams fromthe rod type optical integrator to form a plurality of plane lightsources on the Fourier transformed surface with respect to the reticleor on a plane adjacent to the same.

The operation of the present invention will now be described withreference to FIG. 13. The description will be given hereinafter about anexample of the projection exposure apparatus in which the fly-eye typeoptical integrator (fly-eye lens) is disposed in the irradiation opticalsystem. Referring to FIG. 13, second fly-eye lens groups 40a and 40bcorresponding to the second fly-eye lens according to the presentinvention are disposed on a plane perpendicular to optical axis AX.Light beams emitted from them are incident on first fly-eye lens groups41a and 42b, which correspond to the first fly-eye lens according to thepresent invention, by guide optical systems 42a and 42b. The illuminancedistribution on the incidental surface of the first fly-eye lens is madeuniform by the second fly-eye lens group.

Light beams emitted from the first fly-eye lens group are applied to areticle 9 by a condenser lens 8. The illuminance distribution on thereticle 9 is made to be uniform by the first and the second fly-eye lensgroups to a satisfactory degree. Reticle side focal surfaces 414a and414b of the first fly-eye lens groups 41a and 41b substantially coincidewith a Fourier transformed surface 17 of the reticle pattern 10.Therefore, the distance from optical axis AX to the center of the firstfly-eye lens corresponds to the incidental angle of the light beamsemitted from the first fly-eye lens on the reticle 9.

A circuit pattern 10 drawn on the reticle (the mask) includes amultiplicity of cyclic patterns. Therefore, the reticle pattern 10irradiated with the irradiation light beams emitted from one fly-eyelens group 41a generates a 0-order diffracted light beam component Do,±1-order diffracted light beam components Dp and Dm and higherdiffracted light beam components in a direction corresponding to theprecision of the pattern.

At this time, since the irradiation light beams (the main beams) areincident on the reticle while being inclined, also the diffracted lightbeam components are generated from the reticle pattern 10 while beinginclined (having an angular deviation) in comparison to a case where thereticle 9 is irradiated perpendicularly. Irradiation light beam L130shown in FIG. 13 is incident on the reticle 9 while being inclined by φfrom the optical axis.

Irradiation light beam L130 is diffracted by the reticle pattern 10 andthe 0-order diffracted light beam Do travelling in a direction inclinedby φ from optical axis AX, +1-order diffracted light beam Dp inclinedfrom the 0-order diffracted light beam by θp and the -1-order diffractedlight beam Dm travelling while being inclined from the 0-orderdiffracted light beam Do by θm are generated. However, since irradiationlight beam L130 is incident on the reticle pattern while being inclinedfrom optical axis AX of the double telecentric projection optical system11 by an angle φ, also the 0-order diffracted light beam Do also travelsin a direction inclined by an angle φ from optical axis of theprojection optical system.

Therefore, the +1-order diffracted light beam Dp travels in a directionθp+φ with respect to optical axis AX, while the -1-order diffractedlight beam Dm travels in a direction θm-φ with respect to optical axisAX.

At this time, the diffracted angles θp and θm respectively are expressedby:

    sin (θp+φ)-sin φ=λ/P                  (2)

    sin (θm-φ)+sin φ=λ/P                  (3)

Assumption is made here that both of the +1-order diffracted light beamDp and the -1-order diffracted light beam Dm pass through a pupilsurface 12 of the projection optical system 11.

When the diffraction angle is enlarged with the precision of the reticlepattern 10, the +1-order diffracted light beam Dp travelling in thedirection θp+φ cannot pass through the pupil 12 of the projectionoptical system 11. That is, a relationship expressed by sin(θp+φ)>NA_(R) is realized. However, since irradiation light beam L130 isincident while being inclined from optical axis AX, the -1-orderdiffracted light beam Dm is able to pass through the projection opticalsystem 11 at the aforesaid diffraction angle. That is, a relationshipexpressed by sin (θm-φ)<NA_(R) is realized.

Therefore, interference fringes are generated on the wafer due to the0-order diffracted light beam Do and the -1-order diffracted light beamDm. The aforesaid interference fringes are the image of the reticlepattern 10. When the reticle pattern is formed into a line-and-spacepattern having a ratio of 1:1, the image of the reticle pattern 10 canbe patterned on the resist applied on the wafer 13 while having acontrast of about 90%.

At this time, the resolution limit is present when the followingrelationship is realized:

    sin (θm-φ)=NA.sub.R                              ( 4)

Therefore, the pitch on the reticle side of the minimum pattern whichcan be allowed to be transferred can be expressed by:

    NA.sub.R +sin φ=λ/P

    P≅λ/(NA.sub.R +sin φ)                 (5)

In a case where sin φ is made to be about 0.5×NA_(R), the minimum pitchof the pattern on the reticle which can be transferred becomes asfollows:

    P=λ/(NA.sub.R +0.5NA.sub.R)=2λ/3NA.sub.R     ( 6)

In a case of a conventional exposure apparatus shown in FIG. 14 in whichthe irradiation light beam distribution on the pupil 17 is in a circularregion relative to optical axis AX of the projection optical system 11,the resolution light is P=λ/NA_(R) as expressed by Equation (1).Therefore, the present invention enables a higher resolution incomparison to the conventional exposure apparatus.

Now, the description will be given about the reason why the focal depthcan be enlarged by irradiating the reticle pattern with exposure lightbeams from a specific incidental direction and at a specific angle by amethod in which the image pattern is formed on the wafer by using the0-order diffracted light beam component and the 1-order diffracted lightbeam component.

In a case where the wafer 13 coincides with the focal point position(the best imaging surface) of the projection optical system 11, thediffracted light beams emitted from a point of the reticle pattern 10and reaching a point on the wafer have the same optical path lengthregardless of the portion of the projection optical system 11 throughwhich they pass. Therefore, even in the conventional case where the0-order diffracted light beam component passes through substantially thecenter (adjacent to the optical axis) of the pupil surface 12 of theprojection optical system 11, optical length for the 0-order diffractedlight beam component and that for the other diffracted light beamcomponent are substantially the same and the mutual wavelengthaberration is zero. However, in a defocus state in which the wafer 13does not coincide with the focal point position of the projectionoptical system 11, the optical path length for a higher diffracted lightbeam made incident diagonally becomes short in front of the focal pointin comparison to the 0-order diffracted light beam which passes througha portion adjacent to the optical axis and as well as lengthened in therear of the focal point (toward the projection optical system 11) by adegree corresponding to the difference in the incidental angle.Therefore, the diffracted light beams such as 0-order, 1-order andhigher order diffracted light beams form mutual wave aberration, causingan out of focus image to be generated in front or in the rear of thefocal point position.

The wave aberration generated due to the defocus is a quantity given byΔFr2/2 assuming that the quantity of deviation from the focal pointposition of the wafer 13 is ΔF and the sine of incidental angle θw madewhen each diffracted light beam is incident on one point of the wafer isr (r=sin θw), where r is the distance between each diffracted light beamand optical axis AX on the pupil surface 12. In the conventionalprojection exposure apparatus shown in FIG. 14, the 0-order diffractedlight beam Do passes through a position adjacent to the optical axis.Therefore, r (0-order) becomes 0, while ±1-order diffracted light beamsDp and Dm hold a relationship expressed by r (1-order)=M·λ/P (where M isthe magnification of the projection optical system). Therefore, the waveaberration between the 0-order diffracted light beam Do and ±1-orderdiffracted light beams Dp and Dm becomes:

    ΔF·M2(λ/P)2/2

In the projection exposure apparatus according to the present invention,the 0-order diffracted light component Do is generated in a directioninclined from optical axis AX by an angle φ as shown in FIG. 13.Therefore, the distance between the 0-order diffracted light beamcomponent and the optical axis AX on the pupil surface 12 holds arelationship expressed by r (0-order)=M·sin φ.

The distance between the -1-order diffracted light beam component andthe optical axis on the pupil surface becomes a value obtainable from r(-1-order)=M·sin (θm-φ). If sin φ=sin (θm-φ) at this time, the relativewave aberration between the 0-order diffracted light beam component Doand the -1-order diffracted light beam component Dm due to defocusbecomes zero. Hence, even if the wafer 13 is slightly deviated in thedirection of the optical axis from the focal point position, the out offocus of the image of the pattern 10 can be prevented. That is, thefocal depth can be enlarged. Furthermore, since sin (θm-φ)+sin φ=λ/P asexpressed by the equation (3), the focal depth can be significantlyenlarged by causing the incident angle φ for the irradiation light beamL130 on the reticle 9 to hold a relationship expressed by sin φ=λ/2Pwith the pattern having pitch P.

In the present invention, the irradiation light beams emitted from thelight source are divided into a plurality of light beams before they areintroduced into each fly-eye lens. Therefore, the light beams emittedfrom the light source can be efficiently utilized while reducing loss,so that a projection exposure system revealing high resolution and alarge focal depth can be realized.

As described above, according to the present invention, the necessitylies in simple fact that the irradiation optical system of theprojection exposure apparatus which is being operated is changed at themanufacturing process. Therefore, the projection optical system of anapparatus which is being operated can be utilized as it is and furtherimproved resolution and dense integration can be realized.

Although the irradiation system for use in the present invention becomescomplicated in comparison to an ordinary system, the uniformity of theilluminance on the reticle surface and on the wafer surface can beimproved because the fly-eye lenses are disposed to form two stages inthe direction of the optical axis. By virtue of the two stage fly-eyelens structure, the illuminance uniformity on the reticle and the wafersurfaces can be maintained even if the fly-eye lens is moved on a planeperpendicular to the optical axis.

Since the light dividing optical system efficiently introduces theirradiation light beams to the first stage fly-eye lens, the irradiationlight quantity loss can be satisfactorily prevented. Therefore, theexposure time can be shortened and the processing performance(throughput) cannot deteriorate.

In a system in which the second stage fly-eye lens adjacent to thereticle is made movable as in an embodiment (see FIG. 5), optimumirradiation can be performed in accordance with the reticle pattern.

In a system arranged in such a manner that the first, the second fly-eyelenses and the guide optical system are integrally held while makingthem to be movable, the movable portion can be decreased and thereforethe structure can be simplified. As a result, the manufacturing andadjustment cost can be reduced.

Also in a case where a plurality of the guide optical system and thecorresponding first fly-eye lens are respectively made movable, thelight dividing optical system and the second fly-eye lens group areintegrally held. Therefore, the structure can be simplified and as wellas the manufacturing cost and the adjustment cost can be reduced.

In a system in which the light dividing optical system or a portion ofthe same is made to be movable, the optimum dividing optical system(dividing into two portions and that into four portions can be selected)can be used in accordance with the division conditions.

In a system in which at least a portion of the light dividing opticalsystem can be moved or rotated, the condition of dividing the lightbeams can be varied by, for example, changing the interval between thepolyhedron prisms or by rotating the polyhedron prism. Therefore, avariety of division states can be created by using a small number ofoptical members.

Also in a case where a rod type optical integrator is used in place ofthe fly-eye type optical integrator (the fly-eye lens), or in a casewhere they are combined to each other, an effect similar to theaforesaid structures can be obtained.

Furthermore, the present invention is arranged in such a manner that theirradiation light beams emitted from the light source are divided into aplurality of light beams before a phase difference (the difference inthe length of the optical path) which is longer than the coherentdistance (coherent length) of the irradiation light beams is given to aportion between a plurality of the light beams. The coherent length LSof the irradiation light beam can be expressed by:

    LS=λ2/D1

(where the wave length of the irradiation light beam is λ and its vectorwidth is D1).

That is, if a difference in the optical path length longer than thecoherent length L is present between two light beams emitted from onelight source, the two light beams do not interfere with each other. In acase where the light source is a narrow band KrF excimer laser, thecoherent length L is about 20 mm and therefore an optical pathdifference can be relatively easily given to a plurality of light beams.Therefore, even if a laser having a certain coherence is used, thespeckle interference fringe which can be superposed on the desiredpattern as noise can be effectively reduced. That is, the illuminanceuniformity on the reticle and the wafer can be improved by necessitatinga simple structure in which the optical path difference generatingmember is disposed in the irradiation optical path.

Other and further objects, features and advantages of the invention willbe appeared more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view which illustrates the structure of a first embodimentof a projection exposure apparatus according to the present invention;

FIG. 2 is a view which illustrates a portion of the structure of theirradiation optical system shown in FIG. 1;

FIGS. 3A and 3B are views which illustrate the structure of a prism fordividing the light divider in the irradiation optical system into fourportions;

FIG. 4 is a view which illustrates the structure of a moving mechanismfor fly-eye lens groups;

FIG. 5 is a view which illustrates a modification of a partial structureof the irradiation optical system;

FIG. 6 is a view which illustrates a first modification of the lightdivider in the irradiation optical system;

FIG. 7 is a view which illustrates a second modification of the lightdivider in the irradiation optical system;

FIG. 8 is a view which illustrates a third modification of the lightdivider in the irradiation optical system;

FIG. 9 is a view which illustrates another structure of the irradiationoptical system;

FIGS. 10A to 10D are views which illustrate some structures of theelements of the fly-eye lens;

FIG. 11 is a view which illustrates the principle of the configurationof the fly-eye lenses in the irradiation optical system;

FIGS. 12A to 12D are views which illustrate a method of disposing thefly-eye lenses;

FIG. 13 is a view which illustrates the structure of the apparatus fordescribing the principle of the present invention;

FIG. 14 is a view which illustrates the principle of projectionperformed by a conventional projection exposure apparatus;

FIG. 15 is a view which illustrates the structure of a prism fordividing the irradiation light beams into four portions in theirradiation optical system;

FIG. 16 is a view which illustrates the schematic structure of theirradiation optical system having the prism shown in FIG. 15;

FIG. 17 is a view which illustrates the schematic structure of a secondembodiment of the projection exposure apparatus according to the presentinvention;

FIG. 18 is a view which illustrates the schematic structure of a portionof the irradiation optical system shown in FIG. 17;

FIG. 19 is a view which illustrates a modification of the partialstructure of the irradiation optical system shown in FIG. 17;

FIG. 20 is a view which illustrates a modification of the partialstructure of the irradiation optical system shown in FIG. 17;

FIG. 21 is a view which illustrates a modification of the partialstructure of the irradiation optical system shown in FIG. 17;

FIGS. 22A and 22B are views which illustrate a modification of theoptical path difference generating member in the irradiation opticalsystem;

FIGS. 23A and 23B are views which illustrate an example in which anoptical difference generating member is applied to the projectionexposure apparatus adapted to an annular zone irradiation method;

FIG. 24 is a view which illustrates the structure of a third embodimentof the projection exposure apparatus according to the present invention;

FIG. 25 illustrates a state of a light source image formed on theinjection surface of a polyhedron light source forming optical system;

FIG. 26 illustrates the principle of configuration of the polyhedronlight source forming optical system;

FIG. 27 is a view which illustrates the structure of a fourth embodimentof the projection exposure apparatus according to the present invention;

FIGS. 28A and 28B illustrate an example in which an afocalmagnification-varying optical system is disposed between the input lensand the fly-eye lens in the irradiation optical system;

FIG. 29 is a view which illustrates the structure of a fifth embodimentof the projection exposure apparatus according to the present invention;

FIGS. 30A and 30B are views which illustrate an example of the lightdivider shown in FIG. 29;

FIG. 31 is a view which illustrates a portion of the irradiation opticalsystem shown in FIG. 29;

FIG. 32 is a view which illustrates the structure of a sixth embodimentof the projection exposure apparatus according to the present invention;and

FIG. 33 is a view which illustrates the structure of a seventhembodiment of the projection exposure apparatus according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a first embodiment of the present invention in whichtwo polyhedron prisms are used to form a light dividing optical system.

Irradiation light beams emitted from a light source 1 such as a mercurylamp are gathered by an elliptical mirror 2 before they are made to besubstantially parallel beams by a bending mirror 3 and an input lens 4so that the light beams are incident on light dividing optical systems20 and 21. A light divider according to this embodiment comprises afirst polyhedron prism 20 having a V-shape concave and a polyhedronprism 21 having a V-shape convex. The irradiation light beams aredivided into two light beams by the refraction effect of the aforesaidtwo prisms 20 and 21. The divided light beams are respectively incidenton second fly-eye lenses 40a and 40b.

Although two fly-eye lenses 40a and 40b are used in this embodiment, thequantity of them may be determined arbitrarily. Although the lightdividing optical system is arranged to divide the light beams into twosections to correspond to the number of the second fly-eye lens groups,the light beams may be divided into an arbitrary number of sections tocorrespond to the number of the second fly-eye lens groups. For example,in an arrangement in which the second fly-eye lens group is composed offour lenses, each of the light dividing optical systems 20 and 21 may becomposed of a first polyhedron prism 20 having a pyramid concave and asecond polyhedron prism 21 having a pyramid convex. The irradiationlight beams emitted from the second fly-eye lens groups 40a and 40b arerespectively incident on first fly-eye lens groups 41a and 41b by guideoptical systems 42a, 43a, 42b and 43b. At this time, the first fly-eyelens 41a receives only the light beam travelled from the second fly-eyelens 40a, while the first fly-eye lens 41b receives only the light beamtravelled from the second fly-eye lens 40b.

The light beams emitted from the first fly-eye lenses 41a and 41b areintroduced by condenser lenses 6 and 8 and a bending mirror 7 so as toirradiate a pattern 10 formed on the lower surface of a reticle 9. Thelight beams, which have passed through the pattern 10, are gathered andimaged by a projection optical system 11 so that the image of thepattern 10 is formed on a wafer 13.

It should be noted that reference numeral 12 represents a Fouriertransformed surface (hereinafter called a "pupil surface or plane of theprojection optical system") in the projection optical system 11 withrespect to the pattern 10, the arrangement being sometimes arranged insuch a manner that the pupil surface of the projection optical system isprovided with a variable diaphragm (NA diaphragm).

Also the irradiation optical system includes a pupil surface 17 of theirradiation optical system corresponding to the Fourier transformedsurface with respect to the pattern 10. The reticle side focal surface(emission side focal surface) of each of the aforesaid first fly-eyelenses 41a and 41b is present at a position which substantiallycoincides with the pupil surface 17 of the irradiation optical system.The emission sides of the second fly-eye lenses 40a and 40b are Fouriertransformed surfaces with respect to the incidental surfaces of thefirst fly-eye lenses 41a and 41b by guide optical systems 42 and 48.However, the necessity of strictly maintaining the Fourier transformedrelationship can be eliminated if a relationship can be maintained inwhich the light beams emitted from the respective elements of the secondfly-eye lens in each pair of the fly-eye lenses 40a, 41a, and thefly-eye lenses 40b,41b , are superposed on one another on the incidentalsurface of the first fly-eye lens.

The structure of each fly-eye lens will now be described with referenceto FIG. 10. FIGS. 10A to 10D are enlarged views which illustrate anelement of the fly-eye lens. Actual fly-eye lenses, for example, fly-eyelenses 40a, 40b, 41a and 41b shown in FIG. 1 are aggregates of theaforesaid elements. Some of the elements are arranged (aggregated) in adirection from the upper portion to the lower portion of FIG. 10 and avertical direction to the surface of the drawing sheet to form oneelement.

FIG. 10A illustrates a state where an incidental surface 401a and thelight source side focal surface 403a coincide with each other and anemission surface 402a and a reticle side focal surface 404b coincidewith each other. In the embodiment shown in FIG. 1 and in otherembodiments, the fly-eye lens of the type shown in FIG. 10A is usedunless otherwise specified.

Parallel light beams 410a which have been incident from a light source(in the left portion of the drawing) are gathered to a reticle sidefocal plane 404a as designated by a solid line, while light beams(designated by a dashed line) emitted from one point on the light sourceside focal surface 403a are made to be parallel light beams after theyhave been emitted. Types respectively shown in FIGS. 10B to 10D will bedescribed later.

The light side focal surfaces (which coincide with the incidentalsurfaces here) of the second fly-eye lens groups 40a and 40b and thefirst fly-eye lens group 41a and 41b shown in FIG. 1 hold the imageforming relationship as described above. Therefore, the light beams,which have been incident on the incidental surface of each element of,for example, 40a included by the second fly-eye lens group are imagedand projected on all of the elements of the first fly-eye lens 41a. Thismeans another fact that the light beams from each element of the secondfly-eye lens 40a are superposed on one element included by the firstfly-eye lens 41a. Therefore, the illuminance distribution on theincidental surface of the first fly-eye lens can be made uniform by anintegration effect. Each element included by the first fly-eye lens,thus made uniform, is further integrated (superposed) so as to be usedto irradiate the reticle 9. As a result, a satisfactory illuminanceuniformity can be realized on the reticle 9.

Furthermore, the focal depth of a projected image of the pattern formedin a specific direction and having a pitch of the reticle pattern 10 canbe enlarged extremely because the first fly-eye lens groups 41a and 41bare positioned away from optical axis AX.

However, it is expected that the direction and the pitch of the reticlepattern 10 become different depending upon the employed reticle 9.Therefore, it is preferable that the direction and the pitch are madeoptimum with respect to each reticle 9 by arranging the structure insuch a manner that the positions of the first fly-eye lens groups 41aand 41b and the guide optical systems 42a, 42b, 43a and 43b can bechanged or further the second fly-eye lens groups 40a and 40b and thelight dividing optical systems 20 and 21 can be changed by a drivesystem 56. The drive system 56 is operated in accordance with anoperation command issued from a main control system 50 in such a mannerthat the conditions, such as the position, are set in accordance with aninput made by a keyboard 54. As an alternative to this, a bar codereader 52 may be used to read a bar code pattern positioned on thereticle 9 so as to set the conditions in accordance with readinformation, or the aforesaid irradiation conditions may be written onthe bar code pattern on the reticle 9, or the main control system 50 maypreviously store (previously receive) reticle names and irradiationconditions corresponding to the reticles so as to determine theirradiation conditions by collating the reticle name written on the barcode pattern with the aforesaid contents stored by the main controlsystem 50.

FIG. 2 is an enlarged view which illustrates a portion from the lightdividing optical systems 20 and 21 shown in FIG. 1 to the first fly-eyelens groups 41a and 41b. Assumptions are made here that the surface ofthe first polyhedron prism 20 and that of the second polyhedron prism 21facing each other are parallel to each other, and the incidental surfaceof the prism 20 and the emission surface of the prism 21 areperpendicular to optical axis AX. The first polyhedron prism 20 is heldby a holding member 22, while the second polyhedron prism 21 is held bya holding member 23. The holding members 22 and 23 are held by acorresponding movable member group 24a, 24b and another group 25a and25b in such a manner that the holding members 22 and 23 can be moved ina direction from right to left of the drawing sheet, that is alongoptical axis AX. The aforesaid operation is performed by activatingmembers 27a, 27b, 28a and 28b such as a motor. Since the firstpolyhedron prism 20 and the second polyhedron prism 21 are capable ofindividually moving, the interval between the two emitted light beamscan be radially changed while being centered at a point on optical axisAX by changing the interval between the two prisms 20 and 21.

A plurality of light beams emitted from the polyhedron prism 21 areincident on the second fly-eye lens groups 40a and 40b. In the structureshown in FIG. 2, a group consisting of one of the second fly-eye lensgroups, one of the first fly-eye lens groups, and one of the guideoptical systems 42 and 43 is held by one of the corresponding holdingmember 44a and 44b. Since the holding members 44a and 44b are held bymovable members 45a and 45b, they can be moved with respect to thepositions of stationary members 46a and 46b. The aforesaid operation isperformed by activating members 47a and 47b.

By integrally holding and moving the second fly-eye lens, the firstfly-eye lens and the guide optical system, the positions of the lightbeams emitted from the first fly-eye lens can be arbitrarily changed ina plane perpendicular to optical axis AX while maintaining the opticallypositional relationship between the first fly-eye lens and the secondfly-eye lens. It should be noted that members 48a and 48b projectingfrom the holding members 44a and 44b are light shielding plates. As aresult, stray light beams generated by the light dividing optical systemcan be shielded and a problem that unnecessary light beams reach thereticle can be prevented. Furthermore, the limit present in the movablerange for the holding members 44a and 44b can be reduced since the lightshielding plates 48a and 48b are respectively deviated in the directionalong optical axis AX.

Although the structure shown in FIG. 2 is arranged in such a manner thatthe position of each of the divided light beams can be radially changedwith respect to optical axis AX by changing the optical axialdirectional interval between the light dividing optical systems(polyhedron prisms) 20 and 21, the directions in which light beam passmay be changed in concentrical directions relative to a position onoptical axis AX. FIG. 3 illustrates an embodiment in the aforesaid casein which the holding member 23 for holding the second polyhedron prism(the pyramid prism) 21 is held by a fixing member 25 and the holdingmember 23 can be rotated with respect to the fixing member 25 within thesurface of the drawing sheet drawn on FIG. 3A. The aforesaid rotation iscaused by a drive member 29 such as a motor provided for the fixingmember 29. Furthermore, a gear 30 is disposed adjacent to the holdingmember 23 to correspond to the position of the motor 29. FIG. 3B is across sectional view taken along an arrow 3A shown in FIG. 3A.

The fixing member 25 may be held as shown in FIG. 2 in such a mannerthat it is able to move in the direction of optical axis AX. AlthoughFIG. 3 illustrates the case where the rotation is enabled with respectto the second polyhedron prism 21, an arrangement may be employed inwhich the rotation is also enabled with respect to the first polyhedronprism 20 (with respect to optical axis AX). As an alternative to thestructure in which the polyhedron prisms 20 and 21 are individuallyrotated, the stationary members 26a and 26b shown in FIG. 2 may berotated with respect to another stationary member (for example, anexposure device or the like) relative to optical axis AX. In this case,the rotary mechanism may be arranged, for example, in such a manner thatthe holding member 23 shown in FIG. 3, in place of the polyhedron prism21, holds the stationary members 26a and 26b shown in FIG. 1.

As described above, in a case where the positions of a plurality of thelight beams emitted from the light dividing optical systems 20 and 21are radially or concentrically changed relative to optical axis AX, thepositions of the second fly-eye lens groups 40a and 40b, on which theaforesaid light beams are incident, must be varied in accordance withthe changes in the positions of the light beams. FIG. 4 illustrates anexample of mechanism whereby a two dimensional (in a direction on aplane perpendicular to optical axis AX) operation can be performed. FIG.4 is a view which illustrates the members (the holding members 44a and44b) for integrally holding the second fly-eye lenses 40a and 40b, theguide optical systems 42a, 42b, 43a and 43b and the first fly-eye lenses41a and 41b shown in FIG. 2, viewed from a position adjacent to thereticle in a direction along optical axis AX. Synthetic fly-eye lenses41A, 41B, 41C and 41D are held by corresponding holding members 44A,44B, 44C and 44D which are held by movable members 45A, 45B, 45C and45D, the synthetic fly-eye lenses 41A, 41B, 41C and 41D being able toradially move relative to optical axis AX by activating members 46A,46B, 46C and 46D. The activating members 46A, 46B, 46C and 46D are ableto move on the stationary members 49A, 49B, 49C and 49D in directionssubstantially perpendicular to the aforesaid radial directions (insubstantially concentric directions). Therefore, the synthetic fly-eyelenses 41A, 41B, 41C and 41D are able to be two-dimensionally moved onthe plane (on the surface of the drawing sheet) perpendicular to opticalaxis AX. As a result, the light beams divided by the light dividingoptical system can be efficiently applied to the reticle.

The directions in which the movable members 45A, 45B, 45C and 45D shownin FIG. 4 are moved are not limited to the radial directions relative tooptical axis AX. The directions may be arbitrary directionsperpendicular to optical axis AX. Also in a case where a system can beonly moved one-dimensionally as shown in FIG. 2, the directions may bearbitrary directions perpendicular to optical axis AX.

FIG. 5 illustrates a modification of the guide optical system, whereinall of the guide optical systems 42a, 42b, 43a and 43b are disposedeccentrically with respect to the centers of the second fly-eye lenses40a and 40b and the first fly-eye lenses 41a and 41b.

The positions of irradiation light beams emitted from the second fly-eyelenses 40a and 40b are changed on the plane perpendicular to opticalaxis AX by the eccentric guide optical systems 42a, 42b, 43a and 43bbefore the irradiation light beams are incident on the first fly-eyelenses 41a and 41b.

Furthermore, the positions (the positions on the plane perpendicular tooptical axis AX) of the light beams on the incidental surfaces of thefirst fly-eye lens groups 41a and 41b can be changed by changing thedegree of eccentricity of the guide optical systems 42a, 42b, 43a and43b. The structure shown in FIG. 5 is arranged in such a manner that thechange of the eccentricity amount is performed by activating members421a, 421b, 431a and 431b. The activating members 421a, 421b, 431a and431b enable the guide optical systems 42a, 42b, 43a and 43b via holdingmembers 420a, 420b, 430a and 430b. The incidental surfaces (the left endportion of the drawing) of the second fly-eye lenses 40a and 40b and theincidental surfaces (the left end portion of the drawing) of the firstfly-eye lenses 41a and 41b hold a substantially image formingrelationship. The aforesaid image forming relationship (in a directionalong optical axis AX) cannot be out of order if the operations of theguide optical systems 42a, 42b, 43a and 43b are performed on the planeperpendicular to optical axis AX. Also the first fly-eye lenses 41a and41b are, similarly to the guide optical members, able to move in adirection on the plane perpendicular to optical axis AX by activatingmembers 411a and 411b.

In the system shown in FIG. 5, the light beams emitted from the secondfly-eye lenses 40a and 40b can be moved to arbitrary positions on theplane perpendicular to optical axis AX by the guide optical systems 42a,42b, 43a and 43b. Therefore, the second fly-eye lens groups 40a and 40band the light dividing optical systems 20 and 21 may be stationarilydisposed in place of the arrangement in which they are able to move. Inthe structure shown in FIG. 5, the aforesaid elements are held by acommon holding member 22a. In a case where the arrangement is made tocomprise, as shown in FIG. 5, the guide optical systems 42a, 42b, 43aand 43b and the first fly-eye lens groups 41a and 41b, the lightdividing optical systems 20 and 21 and the second fly-eye lens groups40a and 40b may be arranged to be movable as shown in FIGS. 2 and 3.Although the structure shown in FIG. 5 is arranged in such a manner thatboth the first and the second fly-eye lenses respectively comprise twolenses, the number can be arbitrarily determined.

FIGS. 6, 7 and 8 illustrate modifications of the light dividing opticalsystem. The structure shown in FIG. 6 is composed of concave polyhedronprism 20a and a convex lens (or a lens group having positive power) 21a.Irradiation light beams emitted from an input lens 4 are divided andscattered by the polyhedron prism 20a, and then they are gathered by theconvex lens 21a so that they are incident on the second fly-eye lenses40a and 40b. It should be noted that change of the angle θ1 ofinclination of the inclined surface of the polyhedron prism 20a will, atthe positions adjacent to the second fly-eye lenses 40a and 40b, enablethe positions of the divided light beams to be changed on the planeperpendicular to optical axis AX. For example, an arrangement may beemployed in which two polyhedron prisms 20a and 20b having individualinclination angles θ1 and θ2 are used in such a manner that they can beinterchanged by an activating member 27c. In the above mentionedstructure, the two polyhedron prisms 20a and 20b are held by anintegrated holding member 22a which is held by a movable member 24c. Themovable member 24c is able to move with respect to a stationary member26c by the power of an activating member 27c.

Although the two polyhedron prisms shown in FIG. 6 are arranged in sucha manner that they have the inclined surfaces having individual anglesbut formed in the same direction, the directions may be different fromeach other. As an alternative to this, either of them may have abisectioning V-shape recess and the residual one a pyramid recess. Themechanism for holding the second fly-eye lens groups 40a, 40b, the guideoptical systems 42a, 42b, 43a and 43b and the first fly-eye lens groups41 and 41b is formed similarly to those shown in FIGS. 2, 4 and 5.

FIG. 7 illustrates an example in which an optical fiber 20c is used asthe light dividing optical system. Irradiation light beams incident onan incidental portion 20b of a fiber are divided into two sections byemitting portions 21b and 21c. The emitting portions 21b and 21c areheld by holding members 44c and 44d which also integrally hold thesynthetic fly-eye lens shown in FIG. 2. Hence, the positions of thelight beams can automatically be moved (caused to follow) when thesynthetic fly-eye lenses are moved.

FIG. 8 illustrates an example in which a plurality of mirrors 20d, 21eand 21f are used as the light dividing optical system. A first mirror20d is a V-shape mirror for dividing the light beams into two sections.Second mirrors 21e and 21f are flat mirrors for introducing the lightbeams into the first fly-eye lenses 40a and 40b. This example isarranged in such a manner that the second mirrors 21e and 21f areintegrally held by holding members 44e and 44f which integrally hold thesynthetic fly-eye lens.

In the two examples shown in FIGS. 7 and 8, the holding members 44c,44d, 44e and 44f for holding the lenses are able to move on a plane in adirection perpendicular to optical axis AX similarly to FIG. 2 or 4. Thenumber of the fly-eye lenses and the number of the divided sectionsdivided by the light dividing optical system are not limited to two andare therefore determined arbitrarily. In the structure shown in FIG. 7,the number of the divided sections of the fiber 20c may be changed,while a pyramid mirror (dividing into four sections) may be employed asthe first mirror 20d in the structure shown in FIG. 8.

The structure of the light dividing optical system is not limited to theaforesaid description. For example, diffraction gratings, in particular,phase diffraction gratings, or a convex lens array can be used in placeof the polyhedron prisms 20a and 20b shown in FIG. 6.

FIG. 9 illustrates a modification of the system from the first fly-eyelens groups 41a and 41b to the projection optical system 11. Irradiationlight beams emitted from the emission surface of the first fly-eye lens,that is, from the Fourier transformed surface with respect to thereticle pattern 10, are gathered and shaped by a relay lens 6a. At thistime, a plane which holds an image forming relationship with the reticlepattern 10 is formed by the action of the relay lens 6a. Therefore, theirradiation area on the surface of the reticle pattern can be limited bydisposing a visual field diaphragm (irradiation area diaphragm) 14 onthe aforesaid plane.

Irradiation light beams are applied to the reticle 9 via a relay lens6b, a condenser lens 6c and 8 and a mirror disposed consecutively to thevisual field diaphragm 14. Furthermore, a Fourier transformed surface17b of the reticle pattern 10 appears between the relay lens 6b and thecondenser lens 6c.

Although an aperture diaphragm 5 shown in FIG. 9 is disposed adjacent tothe emission side of the second fly-eye lens, it may be disposedadjacent to the Fourier transformed surface 17b.

Elements of the fly-eye lens for use in the structure according to thepresent invention will now be described with reference to FIG. 10. FIG.10A illustrates the aforesaid structure in which the incidental surface401a, the light source side focal plane 403a, the emission surface 402aand the reticle side focal surface 404a coincide with one another.

However, in the structure shown in FIG. 10A, all of the irradiationlight beams in the element of the fly-eye lens pass through a glasselement and a light converged point is generated in the glass (fly-eyelens). In a case where a pulse laser such as an excimer laser is used asthe light source, energy per pulse becomes excessively large andtherefore there arises risk of breakage of the glass element by theoptical energy in the converged point if the converged point is presentin the glass element.

FIGS. 10B and 10C respectively illustrate examples of the fly-eye lensesfor preventing the aforesaid problem. FIG. 10B illustrates a structurein which both an incidental surface 401b and an emission surface 402bare made of the surfaces of a convex lens, and a reticle side focalsurface 404b is different from an emission surface 402b (a light sourceside focal surface 403b and an incidental surface 401b coincide witheach other). The aforesaid arrangement can be realized by changing thecurvature of the incidental surface 401b and that of the emissionsurface 402b from each other. As a result, the light beams emitted fromthe light source are converged at a point outside the fly-eye lenselement 400b.

FIG. 10C illustrates a modification of the structure shown in FIG. 10B,where a fly-eye lens element 400c has a flat incidental surface 401c.Also in this case, the converged point (a reticle side focal surface404c) can be located outside the lens 400c. Furthermore, the light beamsare not gathered in the lens 400c. However, the light beams except forvertical and parallel beams come in contact with the inner wall of thefly-eye lens 400c and therefore stray beams are generated because theincidental surface 401c has no refraction effect. Therefore, thestructure shown in FIG. 10C will enable an excellent effect to beobtained as the second fly-eye lens in a case where the light sourcecomprises the laser beam source. The reason for this lies in that use ofthe laser beam source will enable the incidental light beams to beparallel beams and to be perpendicularly incident on the first fly-eyelens.

On the contrary, the structure shown in FIG. 10B is suitable when it isused as the first fly-eye lens in a case where the light source is thelaser beam similarly to the structure shown in FIG. 10C.

A fly-eye lens element shown if FIG. 10D is composed of two convexlenses 400d and 400e. The structure is arranged to be different fromthose shown in FIGS. 10A to 10C in such a manner that a space betweenthe two convex lenses 400d and 400e is filled with air or nitrogen orhelium gas. In a case where an exposure wavelength of 200 nm or less isused, it is preferable that the volume of a transmissive solid portionmade of, for example, glass be minimized as shown in FIG. 10D because aproper lens material having satisfactory transmissivity cannot beavailable. In this case, it is preferable to constitute the projectionoptical system by a reflecting optical system (a refractive member maybe partially employed) and also the light dividing optical system mayuse a reflecting mirror arranged as shown in FIG. 8.

A method of optimizing the aforesaid systems to correspond to thereticle pattern to be exposed will now be described. It is preferablethat the position (the position on the plane perpendicular to theoptical axis) of each first fly-eye lens group be determined (changed)in accordance with the reticle pattern to be transferred. In this case,the position may be determined as described above in such a manner thatthe irradiation light beams from the first fly-eye lens groups areincident on the reticle pattern at a position at which the optimumresolution and an effect of improving the focal depth can be obtainedwith respect to the precision (pitch) of the pattern to be transferred.

Specific examples of determining the positions of each first fly-eyelens group will now be described with reference to FIGS. 11 and 12A to12D. FIG. 11 is a view which schematically illustrates a portion fromthe first fly-eye lens groups 41a and 41b to the reticle pattern 10. Inthe structure shown in FIG. 11, reticle side focal surfaces 414a and414b of the first fly-eye lens group 41 coincide with the Fouriertransformed surface 17 of the reticle pattern 10. A lens or a lens groupwhich cause the two elements to hold the Fourier transformationrelationship is expressed by one lens 6. Furthermore, an assumption ismade that both of the distance from the principal point of the lens 6facing the fly-eye lens to the reticle side focal surfaces 414a and 414bof the fly-eye lens group 41 and the distance from the principal pointof the lens 6 facing the reticle to the reticle pattern 10 are f.

FIGS. 12A and 12C illustrate an example of a portion of a pattern to beformed in the reticle pattern 10. FIG. 12B illustrates a position on theFourier transformed surface 17 (on the pupil surface of the projectionoptical system) at the center of the first fly-eye lens group which ismost suitable in the case of the reticle pattern shown in FIG. 12A. FIG.12D illustrates the positions (the positions of the centers of theoptimum fly-eye lens groups) of the fly-eye lens groups which are mostsuitable in the case of the reticle pattern shown in FIG. 12C.

FIG. 12A illustrates a so-called one-dimensional line-and-space patternin which transmissive portions and light shielding portions are arrangedin direction Y while having the same width and furthermore they areregularly arranged in direction X at pitch P. At this time, the optimumpositions for each first fly-eye lens are, as shown in FIG. 12B,arbitrary points on line segments Lα and Lβ assumed on the Fouriertransformed surface. FIG. 12B is a view which illustrates the Fouriertransformed surface 17 with respect to the reticle pattern 10 whenviewed in a direction of optical axis AX, wherein coordinate system Xand Y on the surface 17 is made to be the same as that of FIG. 12A whichillustrates the reticle pattern when viewed in the same direction.

Referring to FIG. 12B, the distances α and β from center C, throughwhich optical axis AX passes, to line segments Lα and Lβ hold arelationship expressed by a α=β which is equal to f·(1/2)·(λ/p).Expressing the distances α and β by f·sin φ, sin φ=λ/2P coincides withthe aforesaid value. Therefore, if each center (each center of gravityof the light quantity distribution of secondary light source images eachof which is formed by the first fly-eye lenses) is positioned on linesegments Lα and Lβ either of ±1-order diffracted light beams generatedfrom the irradiation light beams from each fly-eye lens and 0-orderdiffracted light beam pass through positions of a line-and-space patternshown in FIG. 12A which are the same distance from optical axis AX onthe pupil surface 12 of the projection optical system 11. Hence, thefocal depth with respect to the line-and-space pattern (see FIG. 12A)can be made largest and therefore high resolution can be obtained.

FIG. 12C illustrates a case where the reticle pattern is a so-calledisolated space pattern, wherein the X-directional (in the lateraldirection) pitch of the pattern is Px and the Y-directional (in thelongitudinal direction) pitch of the same is Py. FIG. 12D is a viewwhich illustrates the optimum position for each first fly-eye lens inthe aforesaid case, wherein the positional and rotational relationshipwith FIG. 12C are the same as that between FIG. 12A and 12B. When theirradiation light beams are incident on the two-dimensional patternarranged as shown in FIG. 12C, diffracted light beams are generated inthe two-dimensional direction which corresponds to the periodicity inthe two-dimensional direction of the pattern. Also in thetwo-dimensional pattern arranged as shown in FIG. 12C, the focal depthcan be made maximum by causing either of the ±1-order diffracted lightbeams and the 0-order diffracted light beams to be the same distancefrom optical axis AX on the pupil surface 12 of the projection opticalsystem 11. Since the pitch in the direction X is Px in the pattern shownin FIG. 12C, a maximum focal depth of the X-directional component of thepattern can be obtained if the center of each fly-eye lens is positionedon the line segments Lα and Lβ which hold the relationshipα=β=f·(1/2)·(λ/Px). Similarly, if the center of each fly-eye lens ispresent on line segments Lγ and Lε which hold the relationshipγ=ε=f·(1/2)·(λ/Py), the maximum focal depth of the Y-directionalcomponent of the pattern can be obtained.

As described above, when the irradiation light beams from the fly-eyelens groups disposed at the positions shown in FIG. 12B or 12D areincident on the reticle pattern 10, 0-order diffracted light beamcomponent Do and either +1-order diffracted light beam component DR or-1-order diffracted light beam component Dm pass through the opticalpath on the pupil surface 12 in the projection optical system 11 at thesame distance from optical axis AX. Therefore, a projection exposureapparatus revealing high resolution and a large focal depth can berealized.

Although only the two examples as illustrated in FIGS. 12A and 12C havebeen considered as the reticle pattern 10, another pattern may be usedin such a manner that the center of each fly-eye lens is located at aposition which causes either of +1-order or -1-order diffracted lightbeam component from the pattern and the 0-order diffracted light beamcomponent to pass through the optical path which is located atsubstantially the same distance from optical axis AX on the pupilsurface 12 in the projection optical system. In the example of thepattern shown in FIGS. 12A and 12C, the ratio (duty ratio) of the lineportion and the space portion is 1:1, and therefore ±1-order diffractedlight beams become intensive. Hence, attention is paid to the positionalrelationship between either of the ±1-order diffracted light beams andthe 0-order diffracted light beam. However, in a case where the dutyratio of the pattern is not 1:1 or the like, an arrangement may beemployed in which the positional relationship between another diffractedlight beam, for example, either of ±2-order diffracted light beams andthe 0-order diffracted light beam are allowed to pass through thepositions distant, by the same distance, from optical axis AX on thepupil surface 12 of the projection optical system.

In a case where the reticle pattern 10 has, as shown in FIG. 12D, thetwo-dimensional cyclic pattern, a high order diffracted light beamcomponent higher than 1-order distributed in direction X (in the firstdirection) with respect to one of the 0-order diffracted light beamcomponents and a high order diffracted light beam component higher than1-order distributed in direction Y (in the second direction) can bepresent on the pupil surface 12 of the projection optical system whenattention is paid to a specific 0-order diffracted light beam component.Assuming that the image of a two-dimensional pattern is satisfactorilyformed with respect to one specific 0-order diffracted light beamcomponent, it is necessary for the position of a specific 0-orderdiffracted light beam component (one of the first fly-eye lenses) to beadjusted in such a manner that the three components consisting of one ofthe high-order diffracted light beam component distributed in the firstdirection, one of the same distributed in the second direction and thespecific 0-order diffracted light beam component are distributed by thesame distance from optical axis AX on the pupil surface. For example, itis preferable that the center of the first fly-eye lens be made coincidewith any one of points Pζ, Pη, Pκ and Pμ. Since all of the points Pζ,Pη, Pκ and Pμ are intersections of line segment Lα or Lβ (the optimumportion in terms of the periodicity in the direction X, that is, theposition at which the 0-order diffracted light beam and either of the±1-order diffracted light beam in the direction X are spaced by the samedistance from the optical axis on the pupil surface 12 of the projectionoptical system) and line segments Lγ and Lε (the optimum position interms of the periodicity in the direction Y), the aforesaid position isthe optimum position in either of the directions X and Y.

Although the description has been given while assuming a two dimensionalpattern having the two-dimensional directionality at the same point onthe reticle, the aforesaid method can be adapted to a case where aplurality of patterns having different directionalities are present inthe same reticle pattern.

In a case where the pattern on the reticle has a plurality ofdirectionalities or precisions, the optimum positions for the fly-eyelens groups are the positions which correspond to the directionality ofeach pattern and the precision. As an alternative to this, the firstfly-eye lens may be disposed at the mean position of the optimumpositions. The aforesaid mean position may be the mean load positionobtained by adding weight to the precision or the significance of thepattern.

The 0-order light beam components emitted from the first fly-eye lensare incident on the wafer while being inclined with respect to thewafer. In this case, a problem arises in that the position of thetransferred image is undesirably shifted in a direction on the wafer atthe time of finely defocusing the wafer 13 if the direction of thecenter of gravity of the light quantities of (a plurality of) theinclined incident light beams is not perpendicular to the wafer. Inorder to prevent this, the direction of the center of gravity of thelight quantities on the image forming surface or on its adjacent surfacemust be perpendicular to the wafer, that is, in parallel to optical axisAX.

That is, assuming an optical axis (the center line) for each firstfly-eye lens, the vector sum of the product of the position vector onthe Fourier transformed surface of the optical axis (the center line)with respect to optical axis AX of the projection optical system 11 andthe light quantity emitted from each fly-eye lens must be zero.

A further simple method may be employed in which 2 m (m is a naturalnumber) first fly-eye lenses are used, the positions of m first fly-eyelenses are determined by the aforesaid optimizing method (see FIG. 12)and the residual m first fly-eye lenses are disposed symmetrical tooptical axis AX. The detailed description about the aforesaid structurehas been disclosed in U.S. Pat. Ser. No. 791,138 (filed on Nov. 13,1991) now abandoned.

As described above, when the position of each first fly-eye lens isdetermined, the position (see FIG. 5) of the guide optical system andthe state (see FIGS. 2, 3 and 6) of the light dividing optical systemare determined. The positions and the like of the guide optical system,the light dividing optical system or the second fly-eye lens must bedetermined so as to cause the irradiation light beams to be incident onthe first fly-eye lens most efficiently (in such a manner that the lightquantity loss can be prevented).

In the aforesaid system, it is preferable that each moving portion has aposition detector such as an encoder. The main control system 50 or thedrive system 56 shown in FIG. 1 moves, rotates and exchanges eachelement in accordance with position information supplied from theaforesaid position detector. As for the shape of the lens element foreach fly-eye lens group, the effective area of the reticle or thecircuit pattern area are mainly in the form of a rectangle. Therefore,only the pattern portion of the reticle can be efficiently irradiatedwith light beams in a case where the incidental surface (which holds animage forming relationship with the reticle pattern because the emissionsurface and the surface of the reticle pattern hold the Fouriertransformed relationship and also the incidental surface (light sourceside focal surface) and the emission side (reticle side focal point)hold the Fourier transformed relationship) of each element of the firstfly-eye lens is formed into a rectangular shape to corresponding to theplanar shape of the reticle pattern.

The number of the incidental surfaces of the first fly-eye lens(composed of the aforesaid elements) may be determined arbitrarily. Inthis case, the light quantity loss can be reduced by forming the totalincidental surface into a shape similar to that of the incidentalsurface of one element of the second fly-eye lens. For example, thetotal incidental surface of each first fly-eye lens is made to arectangular shape in a case where the incidental surface of one elementof the second fly-eye lens is formed into a rectangular shape. In a casewhere the incidental surface of one element of the second fly-eye lensis formed into a regular hexagon, the total incidental surface of eachfirst fly-eye lens is formed into a shape which is inscribed in theregular hexagon.

In a case where the image of the shape of the incidental surface of oneelement of the second fly-eye lens is projected by the guide opticalsystem in such a manner that it is somewhat larger than the totalincidental surface of each first fly-eye lens, the effect of makingirradiation uniform at the first fly-eye lens can be further improved.As for the size of the emission surface of each first fly-eye lens, itis preferable that the number of apertures (a single width of the angledistribution on the reticle) per one emitted light beam be about 0.1 toabout 0.3 with respect to the reticle side number of apertures of theprojection optical system. If it is smaller than 0.1 times, thecorrectivity of the pattern transference deteriorates. If it is largerthan 0.3 times, an effect of improving the resolution and that ofrealizing a large focal depth cannot be obtained.

The apparatus according to the aforesaid embodiment may be arranged insuch a manner that the first fly-eye lens groups, the guide opticalsystem and the second fly-eye lens groups (the structure shown in FIG.2) following the light divider can be exchanged for a portion whichcorresponds to a conventional irradiation optical system, that is, astructure formed by integrating the relay lens and one fly-eye lens.

The first embodiment employs a pyramid type prism arranged as shown inFIG. 3 as a light divider for dividing the irradiation light beamsemitted from the light source into four portions. However, another lightdivider except for the pyramid type prism and arranged, for example, asshown in FIG. 15 may be used. The light divider shown in FIG. 15comprises a polyhedron prism (a first prism) 50 having a V-shapedconcave, a prism (a second prism) formed by combining a polyhedron prism51 having a V-shaped convex and a polyhedron prism 20 having a V-shapedconcave, and a polyhedron prism (a third prism) having a V-shapedconvex. That is, two pairs of light dividers, each of which is composedof two V-shaped prisms and which are used in the first embodiment (seeFIG. 2), are arranged in series. Therefore, the irradiation light beamsemitted from the light source 1 are divided into four light beams by therefraction effect of the aforesaid four prisms. Hence, the light beamsare incident on corresponding second fly-eye lenses 40a to 40d (FIG. 1shows only those 40a and 40b).

The first light dividers 50 and 51 divide the irradiation light beamsemitted from the light source 1 while making them substantiallysymmetrical with respect to the direction Y and causing them to havesubstantially the same light quantity. Furthermore, the first lightdividers 50 and 51 emit the two divided light beams in such a mannerthat they travel in parallel to each other (substantially in parallel tooptical axis AX) while being positioned away from each other by apredetermined interval (which corresponds to the X-directional intervalbetween the center of the first fly-eye lens 41a and that of 41d orbetween those 41b and 41c on the pupil surface with respect to thedirection X). On the other hand the second light dividers 20 and 21divide the two light beams divided by the first light dividers 50 and 51while making them substantially symmetrical with respect to thedirection X and causing them to have substantially the same lightquantity. Furthermore, the second light dividers 20 and 21 emit the fourlight beams in such a manner that they travel substantially in parallelto one another (substantially in parallel to optical axis AX) whilebeing positioned away from one another by a predetermined interval(which corresponds to the Y-directional interval between the center ofthe first fly-eye lens 41a and that of 41b or between those 41c and 41don the pupil surface with respect to the direction Y).

Furthermore, the prisms 50 (51 and 20) and 21 are arranged so as to becapable of individually moving along optical axis AX (in a direction Zin case of FIG. 15). Therefore, by adjusting the interval by relativelymoving the first prism 50 and the second prism (51 and 20) in thedirection of the optical axis, the X-directional interval between thetwo light beams emitted from the polyhedron prism 20 can be determinedto be an arbitrary value. Similarly, by adjusting the interval betweenthe second prism (51 and 20) and the third prism 21 by relatively movingthem in the direction of the optical axis, the Y-directional intervalbetween the two pairs of two light beams emitted from the third prism 21can be determined to be an arbitrary value.

There is sometimes a necessity of slightly moving the third prism 21 inthe direction of the optical axis when the optical directional intervalbetween the first prism 50 and the second prism (51 and 20) is changedbecause the polyhedron prisms 51 and 20 are integrally formed with eachother. Although the polyhedron prisms 51 and 20 are integrally formed byadhesion, an arrangement may be employed in which they are able toindividually move in the direction of the optical axis.

As described above, in order to optimize the irradiation condition (inother words, the position of the center of each of the four pairs of thefirst fly-eye lenses on the pupil surface) in accordance with theprecision (the pitch, the linear width, the period and the direction) ofthe pattern for each reticle, the position and the like of the fourpairs of the first fly-eye lenses 41a to 41d can be shifted by the drivesystem. Therefore, in order to cause the four light beams emitted fromthe third prism to be correctly incident on the second fly-eye lenses40a to 40d when the four sets of the first fly-eye lenses 41a to 41d aremoved in accordance with the precision of the reticle pattern, the threeprisms 50, (51 and 20) and 21 are individually moved in the direction ofthe optical axis in synchronization (while following) with the aforesaidmovement.

An arrangement may be employed in which three prisms 50, (51 and 20) and21 are made rotative relative to optical axis AX depending upon thepositions of four sets of the first fly-eye lenses 41a to 41d on thepupil surface 17 so as to be rotated in synchronization with the mutualadjustment of the three prisms in the optical axial direction so thatthe four light beams are incident on the second fly-eye lenses 40a to40d. Another arrangement may be employed in which the three prisms areintegrally constituted on a plane (plane XY of FIG. 15) perpendicular tooptical axis in such a manner that they can be two-dimensionally movedso as to be relatively moved with respect to the irradiation light beamsemitted from the light source on a plane perpendicular to optical axisAX, so that the light quantities of the four light beams emitted fromthe third prism are finely adjusted so as to be substantially the same.In this case, it is preferable that the light quantity of each of thefour light beams to be applied to the reticle 9 is detected by aphotoelectric detector and the aforesaid relative movement is controlledin accordance with the result of the detection. As an alternative to thearrangement in which the three prisms are moved, an arrangement may beemployed in which the position of the irradiation light beam to beincident on the first prism 50 is finely moved by, for example,inclining the parallel and flat glass disposed between the input lens 4(FIG. 1) and the first prism 50.

FIG. 16 is an enlarged view which illustrates a portion from the lightdivider to the first fly-eye lenses 41a to 41d in a case where the lightdivider shown in FIG. 15 is used in the projection exposure apparatus(see FIG. 1). Assumptions are made here that the facing surfaces of thefirst prism 50 between the prism 51 and those between the prism 20 andthe third prism 21 run parallel to each other, and the incidentalsurface of the first prism 50 and the emission surface of the thirdprism 21 are perpendicular to each other. In addition, the joinedsurfaces of the second prisms 51 and 20, that is, the emission surfaceof the prism 51 and the incidental surface of the prism 20 areperpendicular to optical axis AX. Referring to FIG. 16, the samereference numerals as those shown in FIG. 2 are given the same referencenumerals and their descriptions are omitted here.

The first prism 50 is held by the holding member 60, the second prism(51 and 20) is held by the holding member 22, and the third prism 21 isheld by the holding member 23. As an alternative to applying the prism51 and 20 to each other, they may be simply hermetically held orstationarily held while positioning them away from each other by apredetermined interval. The holding member 60 is held by movable members61a and 6lb in such a manner that they are able to move on stationarymembers 26a and 26 in a direction from right to left when viewed in thedrawing, that is, in a direction along optical axis AX. The aforesaidmovement is enabled by activating members 62a and 62b such as motors.

Since the first to third prisms 50, (51 and 20) and 21 are able to moveindividually, the X-, and Y-directional intervals between the four lightbeams emitted to be emitted can be individually adjusted by arbitrarilychanging the mutual distances between the three prisms in the directionof the optical axis. Hence, the positions of the four light beams can bearbitrarily, for example, can be radially changed relative to opticalaxis AX on a plane perpendicular to optical axis AX. For example, in acase where the reticle pattern 10 is a two-dimensional cyclic patternand as well having different X- and Y-directional pitches, the centersof the four sets of the first fly-eye lenses must, on the pupil surface17, coincide with the vertex of the rectangle relative to optical axisAX. Also in this case, by adjusting the mutual intervals between thethree prisms 50, (51 and 20) and 21, the four emitted light beams areenabled to be accurately incident on the corresponding second fly-eyelenses 40a to 40d. Furthermore, the four emitted light beams can beshifted in the concentric directions relative to optical axis AX byarranging the structure in such a manner that the three prisms 50, (51and 20) and 21 can be rotated relative to optical axis AX as describedabove.

Although four sets of the fly-eye lenses are used in the structure shownin FIG. 15, it is sufficient to use two sets of fly-eye lenses in a casewhere the reticle pattern is a one-dimensional cyclic pattern forexample. In this case, two sets of fly-eye lenses are selected from thefour sets and the centers of the two fly-eye lenses are madesubstantially coincide with positions deviated from optical axis AX by aquantity corresponding to the precision of the reticle pattern.

Furthermore, the three prisms are moved in accordance with the positionsof the two second fly-eye lenses, thus selected, in such a manner thatthe two prisms are brought into contact with each other in a hermeticalmanner so as to make either of the distance from the first prism 50 tothe second prism (51 and 20) or the distance from the second prism (51and 20) to the third prism 21 to be zero. In a case where the secondfly-eye lenses 40a and 40b are located substantially symmetric withrespect to optical axis AX and as well as distant from each other by apredetermined distance in the direction X, the second prism (51 and 20)and the third prism 21 are brought into contact with each other in ahermetical manner so as to make the distance to be zero.

As a result, the irradiation light beams emitted from the light source 1are divided into two portions by the first prism 50 and the secondprism, that is the prism 51 and the irradiation light beams are notdivided by the prism 20 and the third prism 21. Hence, the irradiationlight beams emitted from the light source 1 are divided into twoportions by the three prisms while preventing the light quantity lossand they are respectively and collectively incident on the two sets ofthe second fly-eye lenses even if only the two sets of the fly-eyelenses are used.

In a case where a reticle which is not adapted to the inclinedirradiation method, for example, a phase shift reticle of a spatialfrequency modulation type, is used, the irradiation must be performed insuch a manner the light quantity distribution of the irradiation lightbeams on the pupil surface 17 must be limited to a circular (or arectangular) region around the optical axis AX. In this case, the prismsare moved so that the first prism 50 and the second prism (51 and 20),and the second prism (51 and 20) and the third prism 21 are respectivelyare hermetically held so as to make the interval in the direction ofoptical axis AX to be zero. Furthermore, the four sets of the fly-eyelenses are moved so as to be integrated relative to optical axis AX. Asa result, the irradiation light beams emitted from the light source 1are not divided by the three prisms 50, (51 and 20) and 21 but they canbe incident on the four integrated fly-eye lenses while preventing thelight quantity loss. Hence, even if the light divider shown in FIG. 15is used, the conventional irradiation (hereinafter called an "ordinaryirradiation") can be employed. In a case where the four sets of thefly-eye lenses must be moved and integrated (combined), it is preferablethat four sets of holding members be structured in such a manner thatthe four sets of the holding members for integrally holding the firstand the second fly-eye lenses and the guide optical system will not forma gap between contact portions of the four sets of the first fly-eyelenses.

As can be understood from above, the inclined irradiation and theordinary irradiation can easily be changed over while eliminating thenecessity of, for example, changing the optical member in a case wherethe light divider shown in FIG. 15 is used. In case, of the inclinedirradiation, switching can easily be performed between the case in whichthe four sets of the fly-eye lenses are used and the case where the twosets of the fly-eye lenses are used. If a zoom lens system is disposedbetween the input lens 4 and the first prism 50, for example, and aswell if the diameter (the area) of the irradiation light beam to beincident on the first prism 50 can be varied, the light quantity losscan be prevented furthermore and a problem which takes place in that thelight beams emitted from the third prism 21 are concentrically incidenton a portion of the incidental surface of the second fly-eye lens can beprevented. In a case where the four sets of the fly-eye lenses areradially moved relative to optical axis AX for example, a necessitysimply lies in that the diameter of the irradiation light beam to beincident on the first prism 50 is adjusted by the zoom lens system inaccordance with the size (the X- and Y-directional widths) of theincidental surface of each second fly-eye lens. Furthermore, if a zoomlens of the aforesaid type is used, the coherence factor (value) of theirradiation optical system can be varied at the time of performing theordinary irradiation.

A second embodiment of the projection exposure apparatus will now bedescribed with reference to FIGS. 17 and 18. FIG. 17 is a view whichillustrates the schematic structure of the projection exposure apparatusaccording to this embodiment. FIG. 18 is an enlarged view whichillustrates a portion from the light dividers 20 and 21 to the firstfly-eye lenses 41a and 41b. Referring to FIGS. 17 and 18, the sameelements as those shown in FIGS. 1 and 2 are given the same referencenumerals and their descriptions are omitted here.

As shown in FIG. 17, this apparatus according to this embodiment uses,as the exposure light source, a KrF or ArF excimer laser or harmonicwaves such as a metal vapor laser or YAG laser. Therefore, the speckleinterference fringes are prevented and the illuminance uniformity on thewafer is improved by disposing an optical path difference generatingmember (for example, a parallel and flat glass) 70 in the irradiationoptical system. The above mentioned arrangement is different from thefirst embodiment (see FIG. 1) and therefore the description will now begiven about it. It should be noted that a beam shaping optical system 81shown in FIG. 17 includes a Beam expander and the like and capable ofshaping the cross section of the light beam into a proper shape (whichis in the form of a square in usual).

As shown in FIG. 17, the parallel and flat glass 70 serving as theoptical path difference generating member is disposed in either of theoptical paths (in the structure shown in FIG. 17, the optical path forthe light beam to be incident on the second fly-eye lens group 40a) forthe light beams divided by the light dividers 20 and 21. Therefore, thelight beam to be incident on the second fly-eye lens 40a is given aphase delay by a predetermined quantity from the light beam to beincident on the second fly-eye lens group 40b. That is, an optical pathdifference is generated between the two light beams. This embodiment isarranged in such a manner that the thickness of the parallel and flatglass 70 is determined so as to make the optical path difference betweenthe two light beams to be longer than a coherent length LS (LS=λ2/D1).Although the parallel and flat glass 70 is disposed in the optical pathfor either of the two light beams, the parallel and flat glass may bedisposed in each of the optical paths if the optical path differencebetween the two light beams is always longer than the coherent lengthLS. Furthermore, the optical path difference generating member may be,for example, a mirror in place of the parallel and flat glass if it iscapable of turning the light beam to give an optical path difference.

The optical path difference generating member is not limitedparticularly if it is able to give a proper phase difference between thelight beams. The number of the optical paths may be the same number asor a number smaller than the number of the second fly-eye lens groups byone in order to cause a plurality of light beams divided by the lightdivider to have different optical path differences (longer than thecoherent length). For example, in a case where four second fly-eye lensgroups are disposed, the light divider is composed of the firstpolyhedron prism 20 having a pyramid concave and the second polyhedronprism 21 having a pyramid convex (see FIG. 3). Furthermore, four (orthree) parallel and flat glass each having an individual thickness tocorrespond to the coherent length LS may be disposed in the opticalpaths of the light beams in order to cause the four light beams to havedifferent phase differences (optical path differences). The pyramid typeprism may be replaced by a light divider arranged as shown in FIG. 15.

The parallel and flat glass 70, as shown in FIG. 18, is held by theholding member 44a integrally with the first and second fly-eye lenses41a, 40a, and the guide optical systems 42a and 43a. Therefore, when thefirst fly-eye lens is shifted in accordance with the precision, theparallel and flat glass 70 is also moved.

An arrangement may be employed in which the parallel and flat glass 70is not secured to the holding member 44a but it is made to beindividually movable so as to drive the parallel and flat glass 70 insynchronization with the movement of the holding member 44a. By makingthe area of the parallel and flat glass 70 to be larger than the movablerange of the light beams to be incident on the second fly-eye lens group40a on a plane perpendicular to optical axis AX, the necessity of usingthe moving mechanism and the necessity of integrally securing it to theholding member 44a can be eliminated. In this case, the necessity simplylies in that it is mechanically secured to the apparatus.

When the light beams divided by the light dividers 20 and 21 are shiftedto the concentrical direction relative to optical axis AX, it ispreferable that also the parallel and flat glass 70 is rotated relativeto optical axis AX. In a case where a plurality of the light beamsemitted from the light dividers 20 and 21 are shifted in the radialdirection and the concentrical direction relative to optical axis AX,and in particular in a case where the same are shifted in theconcentrical direction, it is preferable that the positions of thesecond fly-eye lens groups 40a and 40b, on which the aforesaid lightbeams are incident, are shifted so as to make coincide the direction ofthe configuration of the elements which constitute the fly-eye lensgroup and the cyclic direction of the reticle pattern to each other. Inthis case, each of the fly-eye lens groups may be made rotative or aplurality of the synthetic fly-eye lenses (the holding members 44a and44b) are made rotative around optical axis AX. The positions of aplurality of the light beams are shifted in the concentrical directionwhen the one-dimensional line-and-space pattern arranged regularly inthe direction X has been changed to a one-dimensional line-and-spacepattern arranged regularly in a direction inclined by 45° from the X andY directions.

A modification of the optical path difference generating memberaccording to the present invention will now be described with referenceto FIGS. 19, 20 and 21. Referring to these drawings, elements having thesame function and operation as those of the elements shown in FIG. 18are given the same reference numerals.

The modification shown in FIG. 19 is arranged in such a manner that theparallel and flat glass is used as the optical path differencegenerating member similarly to the aforesaid embodiment (see FIG. 18),and the parallel and flat glass 70 is disposed in a portion (an upperhalf portion above optical axis AX when viewed in the drawing) of theoptical path for the irradiation light beams which corresponds to eitherof the two inclined surfaces of the light dividers 20 and 21 (theV-shaped prism) prior to the moment the irradiation light beams from thelight source are incident on the light dividers 20 and 21. Therefore,the phase of only the light beam of the two light beams divided by thelight dividers 20 and 21, which is incident on the second fly-eye lensgroup 40a, is delayed so that the optical path difference between thetwo light beams is made longer than coherent length LS. Referring toFIG. 19, the parallel and flat glass 70 is held by a holding member 71and the holding member 71 is held by a movable member 72 so that theparallel and flat glass 70 is able to move with respect to a stationarymember 73. The aforesaid operation is performed by an activating member74. Since the structure is arranged in such a manner that the paralleland flat glass 70 is movable in a direction perpendicular to opticalaxis AX, the parallel and flat glass 70 can be accurately disposed inthe irradiation light beam path while making optical axis AX to be theboundary. Therefore, the phase (the length of the optical path) of onlyeither of the two light beams can be changed. The portions of theapparatus shown in FIG. 19 are basically the same as those of thestructure shown in FIG. 18 and therefore their descriptions are omittedhere. In this modification, the parallel and flat glass 70 may bedisposed at any position in the optical path between a light source 80and the light dividers 20 and 21. As can be clearly seen from FIGS. 18and 19, the parallel and flat glass 70 may be disposed at any positionin the optical path between the light source 80 and the second fly-eyelens groups 40a and 40b. Although it may be disposed in an optical pathbetween the first fly-eye lens groups 41a and 41b and the reticle 9, itmust be disposed at a position at which the light beams from the firstfly-eye lens groups 41a and 41b do not superpose (for example, aposition adjacent to the emission side focal surfaces of the firstfly-eye lens groups 41a and 41b or a position adjacent to theirconjugated surface).

FIG. 20 illustrates a case in which a mirror is used as the optical pathdifference generating member in place of the parallel and flat glass.Also this embodiment is arranged in such a manner that the light beamportion, which corresponds to either of the two light beams to bedivided, is caused to have a phase difference (the difference in theoptical path length) prior to a moment the irradiation light beamsemitted from the light source 80 are incident on the light dividers 20and 21. Referring to FIG. 20, the irradiation light beams emitted fromthe light source 80 are divided into two light beams (the light quantityratio: 1:1) by a beam splitter (a half mirror) 70a. The light beams,which have passed through it, then travel linearly before they areincident on the light dividers 20 and 21. On the other hand, the lightbeams reflected by the half mirror 70a are turned upwards when viewed inthe drawing before they are again turned by the reflecting mirror 70bbefore they are incident on the light dividers 20 and 21. As a result,the light beams reflected by the half mirror 70a are delayed (the phaseis delayed) by the distance from the half mirror 70a to the reflectingmirror 70b. Therefore, also this embodiment enables the optical path ofonly either of the two light beams divided by the light dividers 20 and21 to be changed. The half mirror 70a and the reflecting mirror 70b areintegrally secured by a holding member (omitted from illustration) whilebeing disposed away from each other by a distance with which the opticalpath difference between the two light beams is longer than coherentlength LS. Furthermore, they are disposed in the optical path for theirradiation light beams so as to cause the transmissive light beams andthe reflected light beams from the half mirror 70a to be symmetricallyincident on the light divider 20 with respect to optical axis AX. Sincethis embodiment uses the mirrors 70a and 70b as the optical pathdifference generating members, the irradiation light beams emitted fromthe light source are deflected with respect to optical axis AX of theirradiation optical system as can be understood from FIG. 20. It ispreferable that the structure be arranged in such a manner that themirrors 70a and 70b are able to move in a direction perpendicular tooptical axis AX so as to be able to finely adjust the incidentalpositions at which the transmitted light beams and the reflected lightbeams are incident on the light divider 20. The residual portions of theapparatus shown in FIG. 20 are the same as those of the apparatus shownin FIG. 19.

FIG. 21 illustrates an embodiment in which the structure including theoptical path difference generating members 70a and 70b and the lightdividers 20 and 21 is the same as that shown in FIG. 20 but an imagerotator 75 is further disposed in an optical path for one light beam. Byvirtue of the image rotator 75, only either of the light beams (thereflected light beam in the structure shown in FIG. 21) divided by thehalf mirror 70a is rotated by, for example, 180° on a planeperpendicular to optical axis AX. As a result of the aforesaidstructure, the coherence of the light beams can be further reduced andthe contrast of the speckle interference fringes acting as noisecomponents can be further lowered, causing a satisfactory advantage tobe obtained. The image rotator is not limited to the structure shown inFIG. 21 and constituted by combining prisms.

If the image rotator 75 is disposed in the optical path as in thisstructure, the phase of the reflected light beams is somewhat delayed.Therefore, it is preferable that the distance (the interval) from thehalf mirror 70a and the reflecting mirror 70b be determined. Theposition of the image rotator 75 is not limited to the description aboutthis embodiment, it may be disposed at any position if it is disposed onthe optical path between the light source 80 and the reticle 9 similarto the optical path difference generating member. For example, it may bedisposed in the rear of the light dividers 20 and 21 (adjacent to thesecond fly-eye lens). Furthermore, the image rotator 75 may be disposedmore adjacent to the light source or the second fly-eye lens than theoptical path difference generating member (70 or 70a and 70b). A similareffect can be also obtained in a case where the image rotator 75 isdisposed in the structures shown in FIGS. 18 and 19. In other words, theconditions such as the position and the number required for the imagerotators 75 are the same as those required for the optical pathdifference generating member. In a case where the irradiation lightbeams emitted from the light source 80 are divided into four portions,the image rotors are disposed in the optical paths for three light beamsof the four divided light beams in such a manner that they are rotated90°, 180° and 270° respectively (the residual one is rotated by 0° )from the direction of the optical axis. The image rotors may be disposedin the optical paths for the four light beams in such a manner that theyare rotated by 90°, 180°, 270° and 360° from the direction of theoptical axis.

Also the structure according to this embodiment may employ the lightdivider shown in FIGS. 5 to 8. In a case where the light divider shownin FIGS. 7 and 8 is used, the optical path difference generating member(the parallel and flat glass 70) may be disposed in an optical pathbetween the fiber emission portions 21b and 21c and the second fly-eyelenses 40a and 40b, or in an optical path between the first mirror 20dand the second mirrors 21e and 21f (or the second fly-eye lenses 40a and40b) similarly to the embodiment shown in FIG. 18, or in an optical pathmore adjacent to the light source than the fiber incidental portion 20fand the first mirror 20d similarly to the embodiment shown in FIG. 19.The number of divisions performed by each synthetic fly-eye lens and thelight divider is not limited to two but the divisions may be made by anarbitrary number. In the structure shown in FIG. 7, the number ofdivisions (the number of emission portions) of the fiber 20c may bechanged, while the pyramid mirror (for dividing into four portions) maybe used as the first mirror 21d in the structure shown in FIG. 8.

The aforesaid embodiments are formed into a two-stage integratorstructure in which the two sets of the fly-eye lenses are disposed inseries to receive a plurality of the light beams divided by the lightdividers 20 and 21. However, a square rod type optical integrator may beused as the optical integrator, or two sets of the rod type opticalintegrators are combined to each other, or the rod type opticalintegrator and the fly-eye type optical integrator may be combined toeach other to constitute the aforesaid two-stage integrator structure.An example of employment of the rod type optical integrator has beendisclosed in U.S. Pat. No. 4,952,815. As an alternative to the two-stageintegrator structure, an arrangement may be employed in which each of aplurality of light beams divided by the light dividers 20 and 21 is thendivided into a plurality of light beams by using a polyhedron prism or amirror, and a plurality of the divided light beams are caused to beincident on the incidental surface of one fly-eye lens group (a rod typeintegrator may be used) in a superposed manner.

As a result of the aforesaid structure. the illuminance uniformityimprovement effect can be somewhat obtained by using only one opticalintegrator. Furthermore, by reducing, for example, the size (the crosssectional area) of each element constituting the fly-eye lens, theilluminance uniformity can be improved to a certain degree by using onlyone mesh-type fly-eye lens. Although two sets of fly-eye lenses (40a and41a) and (40b and 41b) are disposed to receive a plurality of the lightbeams divided by the light dividers 20 and 21 in the aforesaidembodiment, either of the first fly-eye lens and the second fly-eye lensmay be formed into one large fly-eye lens which covers a region. throughwhich the light beams pass, on a plane perpendicular to optical axis AX.In this case, it is preferable that size of the fly-eye lens bedetermined while considering the movable range of the light beams on theplane perpendicular to optical axis AX corresponding to the periodicityand the precision of the reticle pattern. This fact is also adapted to acase where only one set of the fly-eye lenses is used. If the lightbeams to be incident on each fly-eye lens in the irradiation opticalsystem shown in FIGS. 18 to 21 and FIGS. 5 to 8 are used to irradiate anarea which is externally wider than the incidental end of each fly-eyelens and if the distribution of the quantity of light to be incident oneach fly-eye lens is uniform, a satisfactory effect can be obtainedbecause the illuminance uniformity on the reticle pattern surface can befurther improved.

As can be seen from the above, regardless of the structure of the lightdivider and that of the fly-eye eye lens, a projection exposureapparatus having the irradiation optical system for forming at least twolight quantity distributions (the second light source image) on thepupil surface 17 of the irradiation optical system or on a planeadjacent to it enables the illuminance uniformity improvement effect tobe obtained on the reticle pattern surface by generating an optical pathdifference longer than coherent length LS between the light beams byusing the optical path difference generating member such as the paralleland flat glass.

In the above mentioned embodiment, the parallel and flat glass 70serving as the optical path difference generating member is disposed inthe optical path for either of the two light beams divided by the lightdividers 20 and 21. However, two parallel and flat glass members eachhaving a thickness which causes the optical path difference between thetwo light beams to be longer than coherent length LS may be disposed inthe optical paths. Furthermore, the two parallel and flat glass membersmay be integrally formed. In a case where the irradiation light beamsare divided into four portions by the light dividers 20 and 21, anoptical member 90 arranged as shown in FIG. 22A may be used which isconstituted by integrally combining parallel and flat glass plates 90ato 90d having different thickness. In this case, the thickness of eachparallel and flat glass is determined so as to make all of the mutualoptical path differences between the light beam which pass through theparallel and flat glass members 90a to 90d to be longer than coherentlength LS. It should be noted that the parallel and flat glass may beomitted from the optical path for one of the four light beams asdescribed above. As an alternative to using the parallel and flat glassas the optical path difference generating member, a stepped prism 91arranged as shown in FIG. 22B may be used. The stepped prism 91 isconstituted by, for example, combining prisms in the form of a squarerod by the same number as that of the elements which constitutes thefly-eye lens. The thickness of each prism is determined so as to makeall of the mutual optical path differences between the light beams whichpass through each prism to be longer than coherent length LS. If theaforesaid stepped prisms 91 is disposed in the optical path for onelight beam, interference generated between elements for the fly-eye lenscan be prevented and therefore the illuminance uniformity can be furtherimproved. Although the optical path difference is generated by makingthe thickness (the length) of the optical member 90 or the stepped prism91 to be different, a similar mutual optical path difference between thelight beams can be generated by constituting each of the parallel andflat glass or the prism by optical material having different refractivefactor as an alternative to employing the different thickness (lengths).

Although the aforesaid embodiment has been described about theprojection exposure apparatus having the irradiation optical system forforming at least two light quantity distributions (the secondary lightsource image of the fly-eye lens) on the pupil surface 17 of theirradiation optical system or on a plane adjacent to it, the illuminanceuniformity on the reticle pattern surface can be expected if the opticalpath difference generating member 90 shown in FIG. 22A is used in aprojection exposure apparatus which is adapted to the annular zoneirradiation method. Now the aforesaid improvement effect will bedescribed in brief with reference to FIGS. 23A and 23B. Referring toFIG. 23A. irradiation light beam IL emitted from a light source (omittedfrom illustration) is incident on a prism 92 so as to be formed into anannular band shape. and then it is incident on a second fly-eye lens 93via the optical path difference generating member 90. The irradiationlight beams pass through a lens 94 and a first fly-eye lens 95 beforebeing used to irradiate the reticle pattern by the condenser lenses 6and 8 (see FIG. 17) with substantially uniform illuminance. Thestructures except for those shown in FIG. 23A are the same as thoseshown in FIG. 17. FIG. 23B illustrates a state where the optical pathdifference generating member 90 shown in FIG. 23A is viewed from thedirection of the optical axis. The prism 92 is a so-called cone prismhaving conical shape inclined incidental surface and the emissionsurface so that the irradiation light beams are formed into the annularband shape by the refraction effect of the prism 92 before they are usedto irradiate the optical path difference generating member 90. Both thefirst and second fly-eye lenses 93 and 95 are large fly-eye lensesextending, on a plane perpendicular to optical axis AX, to cover theregion through which the annular band shape irradiation light beamspass, the first and second fly-eye lenses 93 and 95 having elements, thecross sectional shape of each of which is very small. By employing theaforesaid structure, that is, the two-stage integrator structure and bydividing the annular band shape irradiation light beams into fourportions by the optical path difference generating member 90 and bymaking the mutual optical path difference between the divided lightbeams to be longer than coherent length LS, the illuminance uniformityon the reticle pattern surface can be improved. Although an example inwhich the annular band shape irradiation light beams are divided intofour portions is illustrated in FIG. 23, the number of divisions may bedetermined arbitrarily (however two or more). If the optical pathdifference generating member 90 is rotated relative to optical axis AXduring the exposure operation, the illuminance uniformity can be furtherimproved. In a case where the inner or the outer diameter of the annularband shape irradiation light beams is changed to correspond to theperiodicity or the precision of the reticle pattern, it is preferablethat a plurality of cone prisms having different thicknesses areexchanged by being disposed in the irradiation optical path and the size(the diameter) of the circular irradiation light beams to be incident onthe cone prism 92 can be varied by a variable aperture diaphragm.

A third embodiment of the present invention will now be described withreference to FIG. 24. FIG. 24 illustrates the schematic structure ofthis embodiment of the projection exposure apparatus. Referring to FIG.24, the same elements as those shown in FIGS. 1 and 17 are given thesame reference numerals. Referring to FIG. 24, the irradiation lightbeams radiated from the light source such as a mercury lamp thebrightness point of which is located at a first focal point of anelliptic mirror 2 are gathered at second focal point A1 so as to besubstantially parallel beams by the input lens 4 (the collimator lens)before they are incident on a fly-eye lens 100 serving as the opticalintegrator (a plane light source forming optical system). The fly-eyelens 100 is constituted by an aggregation of a plurality of rod lenselements each having a rectangular cross section (for example, a squarecross sectional shape), the fly-eye lens 100 having emission surface A2disposed to be conjugate with a light source image formed at the secondfocal point position of the elliptic mirror 2. Therefore, a plurality oflight source images by the same number as those of the rod lens elementsconstituting the fly-eye lens 100 are formed on the emission surface A2of the fly-eye lens 10 and a secondary light source is substantiallyformed to serve as the plane light source. An aperture diaphragm 101 isdisposed in the vicinity of the position at which the secondary lightsource is formed. The light beams, which have passed through theaperture diaphragm 101, are converged by a converging lens 102 beforethey are incident on a polyhedron light source forming optical system103. The polyhedron light source forming optical system 103 (a lensarray) is composed of four lens elements (103a, 103b, 103c and 103d)disposed in parallel. Although FIG. 24 illustrates only the lenselements 103a and 103b, the lens elements 103c and 103d are disposed inparallel to the lens elements 103a k and 103b in a directionperpendicular to the surface of the drawing sheet on which FIG. 24 isdrawn. Each of the lens elements 103a, 103b, 103c and 103d has lenssurfaces on both the incidental side and the emission side and isdisposed eccentrically so as to make the distance from its optical axisto optical axis AX of the irradiation optical system to be the same. Theaforesaid lens elements 103a, 103b, 103c and 103d are disposed to maketheir emission surface A3 conjugate with the emission surface A2 of thefly-eye lens 100. Therefore, images (plane light source images) formedby again imaging the secondary light source are, as shown in FIG. 25,formed on the emission side of the polyhedron light source formingoptical system 103 at four positions which are made to be eccentric withrespect to optical axis AX of the irradiation optical system by a numberwhich is the same as that of the lens elements. That is, four planelight sources divided by the four lens elements 103a to 103d are formed.As can be understood from FIGS. 24 and 25, also this embodiment employsthe inclined irradiation method similarly to the first and the secondembodiments, and therefore a plurality of the lens elements 103a to 103dare disposed at the optimum positions to correspond to the precision andthe periodicity of the reticle pattern.

Referring back to FIG. 24, the four light beams formed on the emissionsurface A3 of each of the lens elements 103a, 103b, 103c and 103d aregathered by the condenser lens 8 so as to uniformly irradiate thereticle 9 while making a predetermined angle from optical axis AX of theirradiation optical system. As a result of the inclined irradiation thusperformed, the light beams, which have passed through and diffracted onthe pattern of the reticle 9, are gathered and imaged by the projectionoptical system 11. Hence, the image of the pattern of the reticle 9 isformed on the wafer 13.

It should be noted that the light source image A1 formed by the ellipticmirror 2, the emission surface A2 of the fly-eye lens 100 and theemission surface A3 of the polyhedron light source forming opticalsystem 103 are disposed to be conjugated with the incidental pupilsurface 12 (an aperture diaphragm 12a) of the projection optical systemin the irradiation optical system shown in FIG. 24. In other words, A1and A2 and A3 are Fourier transformed surfaces of the object surfaces(the reticle 9 and the wafer 13). Furthermore, the incidental surface B1of the fly-eye lens 100 and the incidental surface B2 of the polyhedronlight source forming optical system 103 are made conjugate with theobject surfaces (the reticle 9 and the wafer 13).

It is preferable that the position (the position on a planeperpendicular to the optical axis) of each lens element of thepolyhedron light source forming optical system 103 be determined inaccordance with the reticle pattern to be transferred. The method ofdetermining the position is the same as that for determining theposition of the first fly-eye lens according to the first embodiment(see FIGS. 11 and 12). That is, the position (incidental angle φ) on thereticle on which the irradiation light beams supplied from thepolyhedron light source forming optical system 103 are incident may bedetermined so as to obtain the optimum resolution and an effect ofimproving the focal depth in accordance with the precision of thepattern to be transferred.

FIG. 26 schematically illustrates a portion from the polyhedron lightsource forming optical system 103 to the projection optical system 11,wherein the reticle side (rear side) focal planes 104a and 104b of thepolyhedron light source forming optical system 103 coincide with theFourier transformed surface 17 of the reticle pattern 10. The condenserlens 8 for causing them to have the Fourier transformed relationship isillustrated as one lens. Furthermore, both of the distance from the lenselement side (front) principal point of the condenser lens 8 to thereticle side (rear) focal planes (104a and 104b) of the polyhedron lightsource forming optical system 103 and the distance from the reticle side(rear) principal point of the condenser lens 8 to the reticle pattern 10are expressed by f.

As can be understood from FIGS. 11.12 and 26, if optical axes Axa andAxb (that is, the center of gravity of the light quantity distributionof the secondary light source images formed by the lens elements) ofeach lens element of the polyhedron light source optical system 103 arelocated on line segments Lα and Lβ, two beams pass through positionswhich are distant from optical axis AX on the pupil surface 12 of theprojection optical system 11 by substantially same distance, the twobeams being composed of either of ±1-order diffracted light beamsgenerated from the line-and-space pattern (see FIG. 12A) due to theirradiation of the irradiation light beams from each lens element and0-order diffracted light beam. That is, the focal depth with respect tothe line-and-space pattern shown in FIG. 12A can be made maximum and aswell as high resolution can be obtained.

Assuming that half of the distance between optical axes Axa and Axb ofthe corresponding lens elements 103a and 103b in the cyclic direction(in the direction X) of the reticle pattern shown in FIG. 12 is L(=α=β), the focal distance of the emission (rear) side of the condenserlens 8 is f, the wavelength of the irradiation light beam is λ and thepitch of the reticle pattern is P, the two lens elements 103a and 103bmust be structured (disposed) in such a manner that the positions oftheir optical axes Axa and Axb substantially satisfy an equationexpressed by L=λf/2P.

In order to efficiently divide the irradiation light beams from thefly-eye lens 100 into two portions (to form two plane light sources) bythe two lens elements 103a and 103b included in the polyhedron lightsource forming optical system 103, it is preferable that the crosssectional shape of the lens elements in the polyhedron light sourceforming optical system 103 is formed into a rectangle and as well as thecross sectional shape of the rod lens element in the fly-eye lens 100 isformed into a rectangle similar to the overall shape of the polyhedronlight source forming optical system 103. Also the optimum positions forthe four lens elements of the polyhedron light source forming opticalsystem for use in the case of the two-dimensional pattern shown in FIG.12C are the same as those in the first embodiment (see FIG. 12D). Thatis, since the X-directional pitch of the pattern shown in FIG. 12C isPx, the optical axes of the lens elements must be located on linesegments Lα and Lβ which hold γ=ε=f·(1/2)·(λ/Px) as shown in FIG. 12D soas to obtain the maximum focal depth in the X-directional component ofthe pattern. Similary, the optical axes of the lens elements must belocated on line segments Lγ and Lε which hold α=β=f·(1/2)·(λ/Py) so asto obtain the maximum focal depth in the Y-directional component of thepattern.

In order to realize inclined irradiation balanced to an optimum degreeby most efficiently utilizing (most efficiently utilizing the number ofapertures NA of the projection optical system) the size of the Fouriertransformed surface 17 in a case where the pitch in each direction ofthe two-dimensional pattern shown in FIG. 12 is the same (Px=Py=P), itis preferable that the structure be arranged to satisfy the relationshipexpressed by L=λ/2P assuming that half of the distance between theoptical axes of each of the lens elements of the polyhedron light sourceforming optical system 103 in the directions X and Y of each cyclicreticle pattern is L (α=β=γ=ε), the emission side (rear) focal distanceof the condenser lens 8 is f, the wavelength of the irradiation lightbeam is λ and the pitch of the reticle pattern is P.

In this case, assuming that the number of apertures of the projectionoptical system 11 facing the reticle is NAR, half of the distancebetween the optical axes of each lens element of the polyhedron lightsource forming optical system 103 in directions X and Y of each cyclicreticle pattern is L (α=β=γ=ε) and the emission side (rear) focaldistance of the condenser lens 8 is f, the structure may be arranged tomeet the following relationship:

    0.35NAR≦L/f≦0.7NAR

If the relationship becomes smaller than the lower limit of thisequation, the effect obtainable by virtue of the inclined irradiationdeteriorates and therefore high resolution cannot be realized whilemaintaining a large focal depth even if the inclined irradiation isperformed. If the same exceeds the upper limit of the aforesaidequation, a problem arises in that the light beams supplied from aseparated light source formed on the Fourier transformed surface cannotpass through the projection optical system.

A fourth embodiment of the present invention will now be described withreference to FIG. 27. FIG. 27 is a view which illustrates the schematicstructure of this embodiment of the projection exposure apparatus,wherein the elements having the same functions as those of the elementsof the third embodiment shown in FIG. 24 are given the same referencenumerals. The difference from the third embodiment lies in a fact thatan optical function equivalent to the fly-eye lens 100 is realized byusing a converging lens 105, a rod type optical integrator 106 and aconverging lens 107.

In the structure according to this embodiment, the light source imageconverged at the second focal point A1 by the elliptic mirror 2 isrelayed to the incidental surface A2 of a square rod type opticalintegrator 106 by the input lens 4 and the converging lens 105. Thelight beams emitted from the incidental surface All of the rod typeoptical integrator 106 are reflected by the inner surface of the rodtype optical integrator 106 and then they are emitted from the emissionsurface B11. At this time, the light beams emitted from the emissionsurface B11 are substantially emitted as if there are a plurality oflight source images (plane light surface) at the incidental surface A11of the rod type optical integrator 106. As for details of this, refer toU.S. Pat. No. 4,952,815.

The light beams emitted from the rod type optical integrator 106 areconverged by the converging lens 107 so that a plurality of light sourceimages are formed at the emission side (rear) focal point A2. Hence, asubstantially secondary plane light source is formed. Since the aperturediaphragm 101 is disposed at the secondary light source position, thelight beams, which have passed through it, are converged by a converginglens 108. Then, four third plane light sources separated by thepolyhedron light source forming optical system 103 are formed so thatthe reticle 9 is inclined-irradiated in the superposed manner via thecondenser lens 8. As a result of the structure thus arranged, highresolution can be realized while maintaining a large focal depthsimilarly to the third embodiment.

It should be noted that the light source image A1 formed by the ellipticmirror 2, the incidental surface A11 of the rod type optical integrator106, the emission side (rear) focal point position A2 of the converginglens 107 and the emission surface A3 of the polyhedron light sourceforming optical system 103 are disposed to hold the conjugaterelationship with the incidental pupil 12 (the aperture diaphragm 12a)of the projection optical system 12. In other words, A1, A11, A2 and A3are Fourier transformed surfaces of the object surfaces (the reticle 9and the wafer 13). Furthermore, the emission surface B11 of the rod typeoptical integrator 106 and the incidental surface B2 of the polyhedronlight source forming optical system 103 are relayed by the converginglenses 107 and 108 so that they are disposed in conjugation with theobject surface (the reticle 9 and the wafer 13).

As an alternative to the rod type optical integrator constituted bysquare rod optical members, a hollow and square rod reflecting opticalmember constituted by forming a reflecting member into a square rodshape may be used. Furthermore, the cross sectional shape of the rodtype optical integrator is not limited to the rectangular. It may, ofcourse, be formed into a polygonal or cylindrical shape.

The third embodiment shown in FIG. 24 is arranged in such a manner thatthe variable aperture diaphragm 101 the caliper of which can be variedis formed adjacent to the emission surface of the fly-eye lens 100,while the fourth embodiment shown in FIG. 27 is arranged in such amanner that the variable aperture diaphragm 101 is disposed at theemission side (rear) focal point position of the converging lens 107.The variable aperture diaphragm 101 is able to vary the size of thelight source image to be formed on the emission surface of thepolyhedron light source forming optical system 103 by varying itscaliper. Therefore, by controlling the size of the light source image tobe formed on the pupil surface of the projection optical system, theinclined irradiation can be performed with a proper σ value. That is, itis preferable that the size of the light source image formed by eachlens element included by the polyhedron light source forming opticalsystem 103 be made in such a manner that the number of apertures (thesingle width of the angular distribution on the reticle) per emittedlight beam with respect to the number of apertures of the projectionoptical system facing the recticle is about 0.1 to 0.3. If it is smallerthan 0.1 times, the accuracy of the transferred pattern (image)deteriorates. If the same is 0.3 times or more, the effect of obtaininghigh resolution and a large focal depth become unsatisfactory.

The variable aperture diaphragm for varying the value σ may be disposedadjacent to the emission side of the polyhedron light source formingoptical system 103. In this case, it is preferable that a variableaperture diaphragm is used which has variable apertures by the numberwhich is the same as that of the lens elements which constitute thepolyhedron light source forming optical system 103. Furthermore, forexample, a so-called turret system in which a plurality of apertureshaving different calipers are formed in a disc in place of the variableaperture diaphragm and it is rotated as desired may be employed to varythe size of the light source image for the purpose of obtaining anoptimum value σ.

in order to vary the value θ while preventing the shielding operationperformed by the aperture diaphragm, an afocal magnification-varyingoptical system 110 may be disposed in an optical path between the inputlens 4 and the fly-eye lens 100 and the secondary light source image tobe formed by the emission surface A2 of the fly-eye lens 100 may beefficiently varied by the operation of varying the magnificationperformed by the afocal magnification-varying optical system 110.

FIG. 28 illustrates the optical structure more adjacent to the lightsource than the fly-eye lens 100 shown in FIG. 25, wherein the afocalmagnification-varying optical system 110 is composed of a positive firstlens group 110a, a negative second lens group 110b and a positive firstlens group 110c. As shown in FIGS. 28A and 28B, the magnification can bevaried by moving each of the lens groups 110a to 110c so that the sizeof the secondary light source formed on the emission side of the fly-eyelens can be varied while preventing the fact that the light beams areshielded.

Also by virtue of the magnification variation performed by the afocalmagnification-varying optical system 110. the incidental surface (B1) ofthe fly-eye lens is made substantially conjugate with aperture 2a (B2a)of the elliptic mirror with respect to the input lens 4 and the afocalmagnification-varying optical system 110. As a result, the value θ canbe efficiently varied while maintaining the double conjugatedrelationship with the object surface and the pupil surface (Fouriertransformed surface).

in this case, an arrangement may be employed in which information suchas the width of the lines of the reticle is supplied to input means andthe drive system for varying the diameter of the aperture of theaperture diaphragm is driven in accordance with calculated informationso as to automatically obtain the optimum value σ. Furthermore, astructure may be employed in which a bar code or the like havinginformation about the line width of the reticle pattern is fastened tothe reticle, detection means for detecting information is provided andthe drive system for varying the caliper of the aperture diaphragm isdriven in accordance with detected information so as to set an optimumvalue σ.

Although the embodiments shown in FIGS. 24 and 27 are arranged in such amanner that the light beams from a source such as the mercury lamp areconverged by the elliptic mirror and they are made into parallel beamsby the input lens 4, another structure may be employed in which a lightsource such as an excimer laser for supplying parallel beams is used andthe parallel beams from the laser beam source are caused to be incidenton, in the structure shown in FIG. 24, the fly-eye lens 100, or, in thestructure shown in FIG. 27, on the converging lens 105. in particular,in the third embodiment shown in FIG. 24, the shape of the emissionsurface A2 of the fly-eye lens 100 may be formed into a plane becausethe secondary light source image formed on the emission surface A2 ofthe fly-eye lens 110 is a spot light source having substantially noarea. Furthermore, in a case where a light source such as the excimerlaser capable of emitting large output is used, light energy isconcentrated on the emission surface A2 of-the fly-eye lens 100 and theemission surface A3 of each lens element of the polyhedron light sourceforming optical system 103. Therefore, it is preferable that the focalpoint positions of the incidental surfaces B1 and B2 be located in aspace outer than the corresponding emission surfaces A1 and A3 in orderto maintain the durability of the fly-eye lens 100 and the polyhedronlight source forming optical system 103.

Furthermore, in order to realize the optimum inclined irradiation foreach cyclic line width of the recticle pattern under a high irradiationefficiency, it is preferable that the structure be arranged in such amanner that an exchange is enabled for another polyhedron light sourceforming optical system composed of four lens elements having differentsize and the positions of optical axes with respect to the optical axisof the irradiation optical system form the four lens elements whichconstitute the polyhedron light source forming optical system.Furthermore, it is preferable to employ a structure to change thereticle side number of apertures NA of the plane light source formingoptical system (the fly-eye lens) for forming the plane light sourcemore adjacent to the light source than the polyhedron light sourceforming optical system, the NA of the rod type optical integrator 106and that of the converging lens 107.

As a preferred structure for changing-the reticle side number ofapertures NA of the plane light source forming optical system, it ispreferable to employ a zoom lens type fly-eye lens in the structureshown in FIG. 24 or to arrange the structure in such a manner thatexchange can be enabled for another focal distance. It is preferable toarrange the structure in such a manner that exchange is enabled foranother rod type optical integrator having a different thickness andlength from those of the rod type optical integrator 106 in thestructure shown in FIG. 27. In particular, it is preferable to move theconverging lens 105 in the direction of the optical axis by a distancecorresponding to the change in the length of the rod type opticalintegrator when the rod type optical integrator is exchanged.

Furthermore, the illuminance uniformity of a plurality of the planelight sources to be formed by the polyhedron light source formingoptical system 103 may be further improved by disposing another planelight source forming optical system more adjacent to the light sourcethan the polyhedron light source forming optical system 103 in theirradiation optical system according to each embodiment.

A fifth embodiment of the present invention will now be described withreference to FIG. 29. FIG. 29 is a view which illustrates the schematicstructure of this embodiment of the projection exposure apparatus.Referring to FIG. 29, the same elements as those shown in FIG. 1 aregiven the same reference numerals. Referring to FIG. 29, the irradiationlight beams radiated from the light source such as a mercury lamp areconverged by the elliptic mirror 2, and then they are made intosubstantially parallel beams by the input lens (collimator lens) 4before they are incident on the light dividing optical systems 200 and201. The light dividing optical systems are composed of the firstpolyhedron prism 200 having a V-shaped concave and the polyhedron prism201 having a V-shaped convex. As a result of the refraction effect ofthe two prisms, the irradiation light beams are divided into two beams.Each light beam is incident on an individual first plane light sourceforming optical system composed of elements 202a, 203a and 204a and asecond plane light source forming optical system composed of elements202b, 203b and 204b.

Although the two plane light source forming optical systems are used,the number of them may be determined arbitrarily. Furthermore, althoughthe light dividing optical system is divided into two sections tocorrespond to the number of the plane light source forming opticalsystems, the number of divisions may be arbitrary determined tocorrespond to the number of the polyhedron light source forming opticalsystem. For example, the light dividing optical systems 200 and 201 mayrespectively be composed of a first polyhedron prism (see FIG. 30A)having a pyramid concave and a second polyhedron prism (see FIG. 30B)having a pyramid convex.

Each plane light source forming optical system is composed of firstconverging lenses 202a and 202b, rod type optical integrators 203a and203b and second converging lenses 204a and 204b. The light beams dividedinto two portions by the light dividing optical systems 200 and 201 areconverged by the first converging lenses 202a and 202b before they areincident on the rod type optical integrators 203a and 203b. Each of therod type optical integrators 203a and 203b is constituted by a squarerod type optical member having the incidental surface A2 located at theconverging point of the first converging lenses 202a and 202b or at aposition adjacent to it, the incidental surface A2 being disposedsubstantially conjugate with the light source image position A1 of theimage formed by the elliptic mirror 2. The light beams, which have beenincident on the rod type optical integrators 203a and 203b are reflectedby their inner surfaces before they are emitted from the emissionsurface B1. Hence, the emitted light beams from the emission surface B1emit as if there are a plurality of light source images (plane lightsources) on the incidental surface A2. The aforesaid function has beendisclosed in U.S. Pat. No. 4,952,815 in detail.

The irradiation light beams emitted from the rod type opticalintegrators 203a and 203b are converged by the second converging lenses204a and 204b so that two secondary light sources are formed at theemission side (rear) focal point position A3 of the aforesaid lenssystem. Therefore, substantially two plane light sources are formed. Theaperture diaphragm 205 having two apertures is disposed at the positionA3 at which the secondary light sources are formed so that each lightbeam, which has passed through each aperture of the aperture diaphragm205 is converged by the condenser lens 8. As a result, the reticle 9 isinclined-irradiated at a predetermined inclination.

A predetermined circuit pattern is formed on the lower surface of thereticle 9 and the light beams, which have passed through and have beendiffracted by the reticle pattern, are converged and imaged by theprojection optical system 11. As a result, the pattern of the reticle 9is formed on the wafer 13.

In the irradiation optical system shown in FIG. 29, the light sourceimage A1 formed by the elliptic mirror 2, the incidental surfaces A2 ofthe rod type optical integrators 203a and 203b, and the emission side(rear) focal point positions A3 of the second converging lenses 204a and204b are conjugate with the incidental pupil surface 12 (the aperturediaphragm 12a) of the projection optical system 11. In other words, A1,A2 and A3 are Fourier transformed surfaces of the object surfaces (thereticle 9 and the wafer 13). Furthermore, the emission surfaces B1 ofthe rod type optical integrators 203a and 203b are conjugate with theobject surfaces (the reticle 9 and the wafer 13).

As described above, the first plane light source forming optical systemcomposed of the elements 202a, 203a and 204a and the second plane lightsource forming optical systems composed of the elements 202b, 203b and204b are located away from optical axis AX. Therefore, the focal depthof a pattern of the patterns of the reticle 9 having a specificdirection and a pitch can be considerably enlarged.

FIG. 31 is an enlarged view which illustrates a portion from the lightdividing optical systems 200 and 201 to the second converging lenses204a and 204b shown in FIG. 29. Assumptions are made here that thefacing surface of the first polyhedron prism 200 and the secondpolyhedron prism 201 are parallel to each other and the incidentalsurface of the prism 200 and the emission surface of the prism 201 areperpendicular to optical axis AX. Referring to FIG. 31, the sameelements as those shown in FIG. 2 are given the same reference numeralsand their descriptions are omitted here. The first polyhedron prism 200is held by the holding member 23.

A plurality of light beams emitted from the polyhedron prism 201 areincident on the first converging lenses 202a and 202b. Referring to FIG.31, the first plane light source forming optical system composed of theelements 202a, 203a and 204a is held by the holding member 44a, whilethe second plane light source forming optical system composed of theelements 202b, 203b and 204b is held by the holding member 44b.

By integrally holding and moving the first plane light source formingoptical system composed of the elements 202a, 203a and 204a and thesecond plane light source forming optical system composed of theelements 202b, 203b and 204b, the position of the light beams emittedfrom the second converging lenses 204a and 204b can be arbitrarilyshifted on a plane perpendicular to optical axis AX.

Although the structure shown in FIG. 31 is arranged in such a mannerthat the position of each divided light beam can be radially shiftedwith respect to optical axis AX by changing the interval between thelight dividing optical systems (the polyhedron prisms) 200 and 201 inthe optical axial direction, each light beam may be shifted in theconcentrical direction relative to optical axis AX.

Also in this embodiment similarly to the aforesaid embodiments, it ispreferable that the positions (the positions on the plane perpendicularto the optical axis) of the first plane light source forming opticalsystem composed of the elements 202a, 203a and 204a and the second planelight source forming optical system composed of the elements 202b, 203band 204b be determined (changed) in accordance with the reticle patternto be transferred. It is preferable in this case that the method ofdetermining the positions be arranged as described above in such amanner that the positions (incidental angle φ) on which the irradiationlight beams form each plane light source forming optical system areincident on the reticle pattern are determined so as to realize theoptimum resolution and obtain the effect of improving the focal depthwith respect to the precision of the pattern to be transferred. Thedescription about the optimum configuration of the plane light sourceforming optical systems is omitted here. As a result of the aforesaidstructure, also this embodiment enables the focal depth to be madelargest with respect to the reticle pattern while realizing highresolution.

A sixth embodiment of the present invention will now be described withreference to FIG. 32. FIG. 32 is a view which illustrates the schematicstructure of the projection exposure apparatus according to thisembodiment. Referring to FIG. 32, the same elements as those of thefifth embodiment (see FIG. 29) are given the same reference numerals.The difference from the fifth embodiment lies in that fly-eye lenses300a and 300b are disposed in plane of the first converging lenses 202aand 202b.

Referring to FIG. 32, the irradiation light beams radiated from thelight source 1 such as a mercury lamp are converged by the ellipticmirror 2 and then they are made to be substantially parallel beams bythe input lens (the collimator lens) 4 before they are divided by thelight dividing optical systems 200 and 201. The two divided parallelbeams are incident on the fly-eye lenses 800a and 800b made ofaggregates of rod lens elements having a rectangular cross section (forexample, a square cross section) so as to be converged on their emissionsurfaces A2 or portions adjacent to the emission surfaces A2. As aresult, a plurality of spot light sources are formed. The plane lightsource substantially serving as the secondary light source is formed inthe aforesaid position. The incidental surfaces of the rod type opticalintegrators 203a and 203b are located adjacent to the emission surfacesof the fly-eye lenses 300a and 300b. Therefore, the incidental surfacesof the rod type optical integrators 203a and 203b are disposedsubstantially conjugate with the light source image position A1 of theimage formed by the elliptic mirror 2. The rod type optical integrators203a and 203b are made of rectangular rod shape optical members so thatthe incidental light beams are reflected by their inner surfaces andemitted from the emission surface B1 as described above. Hence, thelight beams are emitted from the emission surface B1 as if there are aplurality of the light source images (the plane light source) on theaforesaid incidental surface A2.

The irradiation light beams emitted from the rod type opticalintegrators 203a and 203b are converged by the converging lenses 204aand 204b so that two plane light source images serving as the thirdlight sources are formed at eccentric positions from optical axis AX atthe emission side focal point position of the lens. Therefore, theilluminance distribution of the light beams on the emission surfaces ofthe fly-eye lenses 300a and 300b are made uniform by the integrationeffect. Furthermore, the light beam illumination distribution at theemission side focal point position A3 of the converging lenses 204a and204b can be further satisfactorily made uniform by the rod type opticalintegrators 203a and 203b.

The aperture diaphragm 205 having two apertures is disposed at theposition A3 at which the two plane light sources serving as the thirdlight sources are formed. Each light beam which has passed through theaperture diaphragm 205 is converged by the condenser lens 8 so that itis used to uniformly irradiate the reticle 9 at a predetermined angle.The light beams which have passed through and been diffracted by thereticle pattern in the inclined irradiation manner are converged andimaged by the projection optical system 11, so that the image of thepattern of the reticle 9 is formed on the wafer 13.

As described above, the first plane light source forming optical systemcomposed of elements 300a, 203a and 204a and the second plane lightsource forming optical system composed of elements 300b, 203b and 204bare disposed away from optical axis AX. Therefore. the focal depth ofthe projected image of the pattern of the patterns of the reticle havinga specific direction and pitch can be considerably enlarged.

In the irradiation optical system shown in FIG. 32, the light sourceimage A1 formed by the elliptic mirror 2, the emission surfaces (theincidental surfaces of the rod type optical integrators 203a and 203b)A2 of the fly-eye lenses 300a and 300b and the emission side focal pointpositions A3 of the second converging lenses 204a and 204b are conjugatewith the incidental pupil 12 (the aperture diaphragm 12a) of theprojection optical system 11. In other words, A1, A2 and A3 are Fouriertransformed surfaces of the object surfaces (the reticle 9 and the wafer13). Furthermore, the incidental surfaces B11 of the fly-eye lenses 300aand 300b and the emission surfaces B1 of the rod type opticalintegrators 203a and 203b are conjugate with the object surfaces (thereticle 9 and the wafer 13).

Although the sixth embodiment shown in FIG. 32 is arranged in such amanner that the light beams are divided into two portions by the lightdividing optical systems 200 and 201, another structure may be employedin which the prism shown in FIG. 30 is used and four plane light sourceforming optical systems are disposed in parallel to correspond to theprism facing the reticle so as to form four plane light sources on theFourier transformed surface.

A seventh embodiment of the present invention will now be described withreference to FIG. 33. Referring to FIG. 33, the same elements as thoseof the fifth embodiment shown in FIG. 29 are given the same referencenumerals. The difference from the fifth embodiment lies in that thefunction equivalent to that realized by the first plane light sourceforming optical systems composed of the elements 300a, 203a and 204a andthe second plane light source forming optical system composed of theelements 300b, 203b and 204b is realized by one optical system composedof the first converging lens 210, the rod type optical integrator 211and the second converging lens 212.

Referring to FIG. 33, the irradiation light beams radiated from thelight source i such as a mercury lamp are converged by the ellipticmirror 2 and then they are made to be substantially parallel beams bythe input lens (the collimator lens) 4 before they are divided into twoportions by the light dividing optical systems 200 and 201. The twodivided parallel beams are converged to the emission side (rear) focalpoint position by the first converging lens 210. The incidental surfacesof the rod type optical integrator 211 is located at the focal pointposition A2, the incidental surfaces being substantially conjugate withthe light source image position A1 of the image formed by the ellipticmirror 2.

As described above, the light beams which have been incident on the rodtype optical integrator 211 are reflected by the inner surface of itbefore they are emitted from the emission surface B1. Therefore, thelight beams are emitted from the emission surface B1 as if there are aplurality of the light source images (the plane light sources) on theincidental surface A2. Then, the light beams are converged by the secondconverging lens 212 so that two plane light source images separated fromeach other and serving as the secondary light sources are formed at theemission side (rear) focal point position A3 of the lens 212. The reasonfor this lies in a fact that the light beams are incident on the rodtype optical integrator in a state where they are separated from eachother while making the same angle.

The aperture diaphragm 205 having two apertures is disposed at theposition A3 at which the two plane light source images serving as thesecond light source are formed. The light beams which have passedthrough the aperture diaphragm 205 are converged by the condenser lens 8so that the reticle 9 is uniformly irradiated with them while beinginclined at a predetermined angle. A predetermined circuit pattern isformed on the lower surface of the reticle 9 so that the light beamswhich have passed through and been diffracted by the reticle pattern bythe inclined irradiation method are converged and imaged by theprojection optical system 11. Hence, the image of the pattern of thereticle 9 is formed on the wafer 13.

As described above, the positions of the centers of gravity of the twoplane light sources (the secondary light sources) formed by thepolyhedron light source forming optical systems 210, 211 and 212 arelocated distant from optical axis AX. Therefore, the focal depth of theprojected image of the pattern of the patterns of the reticle 9 having aspecific direction and pitch can be considerably enlarged.

According to this embodiment, by only changing the air interval betweenthe two polyhedron prisms which constitute the light dividing opticalsystems 200 and 201, the incidental angle of the divided light beams tobe incident on the incidental surface A2 of the rod type opticalintegrator can be varied. Hence, the position of the secondary lightsource image to be formed on the emission side (rear) focal pointposition A3 of the second converging lens 212 with respect to opticalaxis AX of the secondary light source image can be controlled.

In the irradiation optical system shown in FIG. 33, the light sourceimage A1 formed by the elliptic mirror 2. the incidental surface A2 ofthe rod type optical integrator 211 and the emission side focal pointposition A3 of the second converging lens 212 are conjugate with theincidental pupil 12 (the aperture diaphragm 12a) of the opticalprojection system 11. In other words, A1, A2 and A3 are Fouriertransformed plane of the object surface (the reticle 9 and the wafer13). Furthermore, the emission surface B1 of the rod type opticalintegrator 211 is conjugate with the object surface (the reticle 9 andthe wafer 13).

Although the seventh embodiment shown in FIG. 33 is arranged in such amanner that the light beams are divided into two portions by the lightdividing optical systems 200 and 201, another structure may be employedin which the prism shown in FIG. 30 is used to form four plane lightsources on the Fourier transformed surface.

In the embodiments shown in FIGS. 29, 32 and 33, the variable aperturediaphragms 205 disposed at the two or three dimensional plane lightsource position formed by each polyhedron light source forming opticalsystem are able to vary the size of the light source image by varyingthe caliper of the variable aperture diaphragm 205. Therefore, bycontrolling the size of the light source image to be formed on the pupilsurface of the projection optical system 11, the optimum inclinedirradiation with a proper value σ can be performed.

As for the size of the plane light source image to be formed by eachpolyhedron light source forming optical system, it is preferable thatthe number of apertures (a single width of the angle distribution on thereticle) per one emitted light beam be about 0.1 to about 0.3 withrespect to the reticle side number of apertures of the projectionoptical system. If it is smaller than 0.1 times, the correctivity of thepattern transference deteriorates. If it is larger than 0.3 times, aneffect of improving the resolution and that of realizing a large focaldepth cannot be obtained.

As an alternative to the variable aperture diaphragm, a so-called turretsystem may be employed in which a disc having a plurality of aperturesRaving different calipers is used so as to be rotated as desired for thepurpose of obtaining the optimum value σ by changing the size of thelight source image.

In the embodiments shown in FIGS. 29, 32 and 33, the structure isarranged in such a manner that the light beams form the light source 1such as a mercury lamp are converged by the elliptic mirror 2 so as tomake them the parallel beams by the input lens 4. As an alternative tothis, an epoxy laser or the like for supplying parallel beams may beemployed as the light source to cause the parallel light beams from thelaser beam source to be incident on the light dividing optical systems200 and 201. In particular, in the sixth embodiment shown in FIG. 32,spot light sources having substantially no size are formed as the lightsource image to be formed on the emission surfaces A2 of the fly-eyelenses 300a and 300b and therefore the shape of the emission surfaces A2of the fly-eye lenses 300a and 300b may be formed into a flat shape. Ina case where a large output light source such as the excimer laser isused, optical energy is concentrated on the emission surfaces A2 of thefly-eye lenses 300a and 300b. Hence, it is preferable that the focalpoints of the incidental surfaces B1 of the fly-eye lenses 300a and 300bare located in a space outside the emission surface A1 in order tomaintain the durability of the fly-eye lenses 300a and 300b.

Although the invention has been described in its preferred form with acertain degree of particularly, it is understood that the presentdisclosure of the preferred form may be changed in the details ofconstruction and the combination and arrangement of parts withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:
 1. A projection exposure apparatus comprising:anillumination optical system for irradiating a mask, said illuminationoptical system including:a light source; first plural fly-eye typeoptical integrators, which are separated from each other, of whichrespective optical axis are spaced from an optical axis of saidillumination optical system in a plane which has a Fourier transformrelationship substantially with respect to a pattern of said mask; alight condensing optical system for collecting light emerging from eachof said first plural fly-eye type optical integrators to supplycollected light to said mask; second plural fly-eye type opticalintegrators, which are separated from each other, of which exit focalplanes are placed in a plane which has a Fourier transform relationshipsubstantially with respect to incident focal planes of said first pluralfly-eye type optical integrators, said second plural fly-eye typeoptical integrators being the same in number as said first pluralfly-eye type optical integrators and disposed so that light from eachsecond fly-eye type optical integrator enters only an associated onefirst fly-eye type optical integrator; and a light divider for dividinglight from said light source into plural light beams and disposed sothat light beams enter said second fly-eye type optical integrators,respectively; and a projection optical system for projecting an image ofthe pattern of the mask on a substrate.
 2. An apparatus according toclaim 1, wherein said illumination optical system further comprises aplurality of optical elements the same in number as said first pluralfly-eye type optical integrators, and wherein image beams from lightsource images formed on an exit focal plane of one of said secondfly-eye type optical integrators are superimposed at an incident surfaceof the associated one of said first fly-eye type optical integrators bya corresponding one of said optical elements.
 3. An apparatus accordingto claim 2, further comprising plural holding members separately movableon a plane perpendicular to the optical axis of said illuminationoptical system, each of said plural holding members holding one of apair of said first and second fly-eye type optical integrators and anassociated one of said optical elements as a unit.
 4. An apparatusaccording to claim 3, further comprising an adjusting device foradjusting said light divider interlocked with a movement of said pluralholding members so that light beams enter said second fly-eye typeoptical integrators, respectively.
 5. An apparatus according to claim 4,wherein said light divider comprises a plurality of polyhedron prisms,and said adjusting device has a driving member for rotating saidplurality of polyhedron prisms in a plane perpendicular to the opticalaxis of said illumination optical system or for moving said plurality ofpolyhedron prisms relatively to each other along the optical axis.
 6. Anapparatus according to claim 3, further comprising a driving device formoving each of said plural holding members in said plane perpendicularto the optical axis of said illumination optical system in accordancewith a fineness of the pattern of said mask.
 7. A projection exposureapparatus comprising: an illumination optical system for irradiating amask, said illumination optical system including:a light source; firstplural optical integrators, which are separated from each other,disposed in respective locations which are spaced from an optical axisof said illumination optical system; a light condensing optical systemfor collecting light emerging from each of said first plural opticalintegrators to supply the collected light to said mask; second pluraloptical integrators, which are separated from each other, said secondplural optical integrators being the same in number as said first pluraloptical integrators and disposed so that light from each of said secondoptical integrators enters only an associated one of said first opticalintegrators; and a light divider for dividing light from said lightsource into plural light beams and disposed so that plural light beamsenter said second optical integrators; and a projection optical systemfor projecting an image of the pattern of the mask on a substrate.
 8. Anapparatus according to claim 7, wherein at least either of said firstplural optical integrators and said second plural optical integratorsare fly-eye optical integrators.
 9. An apparatus according to claim 7,wherein at least either of said first plural optical integrators andsaid second plural optical integrator are rod type optical integrators.10. An apparatus according to claim 7, wherein all of the first pluraloptical integrators are fly-eye type and all of the second pluraloptical integrators are rod type.
 11. An apparatus according to claim 7,wherein said light divider is a polyhedron prism.
 12. An apparatusaccording to claim 7, further comprising:an image rotator disposed in anoptical path for at least any one of a plurality of light beams emittedfrom said light divider.
 13. An apparatus according to claim 7, whereinsaid first and second plural optical integrators are fly-eye typeoptical integrators, and further comprising:a driving device for movingpairs of optical integrators, each pair including a first opticalintegrator and a second optical integrator, for aligning exit focalplanes of said first plural optical integrators with a plane which has aFourier transform relationship substantially with respect to the patternof said mask; and an adjusting device for adjusting said light dividerinterlocked with a movement of at least one of said pairs so that lightbeams enter said second optical integrators, respectively.
 14. Aprojection exposure apparatus comprising:an illumination optical systemfor irradiating a mask, said illumination optical system including:afirst optical integrator; a second optical integrator of which an exitfocal plane is placed in a plane which has a Fourier transformrelationship substantially with respect to an incident focal plane ofsaid first optical integrator; an optical device for forming increasedlight intensity distribution relative to, and within areas outside of, across-like portion defined to intersect at an optical axis of saidillumination optical system, in a focal plane of said first opticalintegrator; and a projection optical system for projecting an image of apattern of said mask on a substrate.
 15. An apparatus according to claim14, wherein said first and second optical integrators are fly-eye typeoptical integrators, and an exit focal plane of said first opticalintegrator is placed in a plane which has a Fourier transformrelationship substantially with respect to said pattern.
 16. Anapparatus according to claim 14, wherein said first optical integratorcomprises plural fly-eye type optical integrators of which exit focalplanes are disposed in a plane which has a Fourier transformrelationship substantially with respect to said pattern, said pluralfly-eye type optical integrators forming a plurality of images of alight source on each of said areas, whereby each light intensity at saidareas is enhanced relative to the intensity at said cross-like portion.17. An apparatus according to claim 14, further comprising a correctingdevice for changing locations of said areas in a plane which has aFourier transform relationship substantially with respect to saidpattern in accordance with a fineness of the pattern of said mask. 18.An apparatus according to claim 17, wherein said optical device has alight divider for dividing light from a light source into plural lightbeams, and said correcting device has an adjusting device for drivingsaid light divider to change locations of said plural light beams fromsaid light divider in a plane perpendicular to the optical axis of saidillumination optical system.
 19. A projection exposure apparatuscomprising:a light source; an illumination optical system fortransforming light from said light source into at least one pair oflight beams symmetrically inclined to a perpendicular to a patternsurface of a mask and for directing the light beams to said mask so thata first-order diffracted light beam and a zero-order diffracted lightbeam occurring from at least a portion of a pattern of said mask aresubstantially symmetrically disposed with relation to the perpendicularto the pattern surface of said mask; two groups of optical integratorsarranged along an optical axis of said illumination optical system forallowing said at least one pair of light beams to pass therethrough; anda projection optical system having an optical axis perpendicular to thepattern surface of said mask for projecting an image of the pattern ofsaid mask on a substrate.
 20. An apparatus according to claim 19,wherein each group of said two groups of the optical integratorsincludes a plurality of optical integrators disposed in respectivelocations which are spaced from the optical axis of said illuminationoptical system a distance in accordance with a fineness of the patternof said mask, and each light beam of said at least one pair of lightbeams passes through an associated one of said plurality of opticalintegrators.
 21. An apparatus according to claim 19, further comprisinga correcting device for changing an incident angle of said at least onepair of light beams with respect to said mask in accordance with afineness of the pattern of said mask.
 22. An apparatus according toclaim 21, wherein said correcting device has an optical member forchanging locations of said at least one pair of light beams in a planewhich has a Fourier transform relationship substantially with respect tothe pattern of said mask.
 23. A projection exposure apparatuscomprising:an illumination optical system for irradiating a patternhaving components along orthogonal first and second directions, saidillumination optical system including: a first optical integrator forforming off-axis secondary light sources in quadrants separated by axesin said first and second directions, in a plane which has a Fouriertransform relationship substantially with respect to said pattern; and asecond optical integrator of which an exit focal plane is disposed in aplane which has a Fourier transform relationship substantially withrespect to an incident focal plane of said first opticalintegrator;wherein said first optical integrator comprises pluralfly-eye type optical integrators, which are separated from each other,of which exit focal planes are substantially disposed in said secondarylight sources.
 24. A projection exposure apparatus comprising:a lightsource; first plural optical integrators, which are separated from eachother, of which exit focal planes are disposed in a plane which has aFourier transform relationship substantially with respect to a patternof a mask; a condenser lens for irradiating said mask with light beamsfrom each of said first plural optical integrators; a second opticalintegrator of which an exit focal plane is disposed in a plane which hasa Fourier transform relationship substantially with respect to incidentfocal planes of said first plural optical integrators; and an opticalmember for receiving light from said light source and emitting plurallight beams that enter respective areas different from each other in anincident surface of said second optical integrator.
 25. A projectionexposure apparatus comprising:a light source; a first optical integratorof which an exit focal plane is disposed in a first plane which has aFourier transform relationship substantially with respect to a patternof a mask; a condenser lens for irradiating said mask with light beamsfrom said first optical integrator; second plural optical integrators,which are separated from each other, of which exit focal planes aredisposed in a second plane which has a Fourier transform relationshipsubstantially with respect to an incident focal plane of said firstoptical integrator so that plural images of said light source arerespectively formed on plural specific areas, which are separated fromeach other, in said first plane; and a light divider for receiving lightfrom said light source and emitting plural light beams that enter saidsecond plural optical integrators, respectively.
 26. A projectionexposure apparatus which forms on a substrate an image of a patternhaving components along orthogonal first and second directions, saidapparatus comprising:plural off-axis first optical integrators which aredisposed in quadrants separated by axes in said first and seconddirections; and plural off-axis second optical integrators which aredisposed so that light beams from one of the second optical integratorsare superimposed at an incident surface of an associated one of saidfirst optical integrators.
 27. An apparatus according to claim 26,wherein said first optical integrators are fly-eye type opticalintegrators, and further comprising:a driving device for moving saidfirst optical integrators for disposing exit focal planes thereof in aplane which has a Fourier transform relationship substantially withrespect to said pattern.
 28. A projection exposure apparatuscomprising:four first fly-eye lenses which are disposed in quadrantsseparated by orthogonal first and second axes; and four second fly-eyelenses of which exit focal planes are disposed in a plane which has aFourier transform relationship substantially with respect to incidentfocal planes of said first fly-eye lenses.
 29. A projection exposureapparatus comprising:an illumination optical system that illuminates apattern of a mask with light from at least one pair of off-axis opticalintegrators, said illumination optical system including a member thatsuperimposes light beams at each incident surface of said opticalintegrators; and a projection optical system for projecting an image ofsaid pattern on a substrate; wherein a 0-order diffracted beam producedfrom said pattern by the irradiation of first light from one of saidpair of optical integrators is directed to said substrate through a sameoptical path of said projection optical system as a diffracted beamproduced from said pattern by the irradiation of second light from theother of said pair of optical integrators.
 30. An apparatus according toclaim 29, wherein the last-mentioned diffracted beam is a 1-orderdiffracted beam.
 31. An apparatus according to claim 29, wherein saidmember comprises a fly-eye type optical integrator.
 32. A microdevicemanufactured by using an apparatus as defined in claim 29.